(via Gemmology Queensland, Vol.3, No.2, February 2002/ GZ English language translation) Dr Karl Schmetzer / Martin P Steinbach writes:
A new method for synthetically altering precious gems was discovered only recently. In this case it is a method of synthetically creating asterism in natural materials, cut as a cabochon. Up until now, the creation of synthetic asterism, e.g. by diffusion treatment of sapphires, was only applied to precious gems if these precious gems also produced natural star stones.
A new study by S F McClure and J I Koivula, titled A new method of imitating asterism in Gems & Gemology, Vol. 37, No.2, 2001, pp 124-128, now describes precious gem minerals with synthetic asterism, although the gems themselves (sinhalite, cassiterite and samarskite) do not produce star stones naturally. Synthetic asterism is also described for minerals, which have produced natural star stones such as garnet, chrysoberyl or rutile.
According to McClure and Koivula, the new type of synthetic asterism is created by orientated series of scratches on the surfaces of the precious gems, cut as cabochon, in which the scratches run parallel to each other. Although details of the treatment method are as yet unknown, it is assumed that the scratches are applied to the surface of the cabochon by hand, whereby the number of series of parallel scratches defines the number of arms in the synthetic stars.
Although it has been known since the 19th century that asterism can be created in metal plates, for example, through oriented scratches, this method had not yet been applied to natural precious gems in order to create synthetic asterism. A detailed treatment of the topic of asterism on even metal sheets is contained in a study penned by W Maier titled Experimental Asterism in the New Journal for Mineralogy, Geology and Paleontology, Vol.78, part 3, 1943, pp 283-380. This article also describes two other examples of synthetic asterism in natural precious gems.
The author purchased the two cabochons from a dealer. The seller claimed that the stones originated from India or Sri Lanka. The first cabochon with synthetic asterism that was examined was a reddish brown cabochon of 3.08 ct. Absorption spectroscopy revealed a spectrum with a series of iron bands, which are typical for the members of the mixed crystal family pyrope/almandine garnet. The microscopic examination of the transparent, actually very pure stone reveals only a few rutile needles, running at a slant to the surface of the cabochon. The orientation and in particular the low number of these rutile needles meant that they most certainly did not contribute to the asterism observed in this stone. The star itself is made up of nine (9) sharp lines of light, caused by nine series of parallel scratches on the surface of the garnet cabochon. In general, four-arm asterism and more rarely six-arm asterism have been described as occurring naturally in various deposits of garnet. A star with nine arms is incompatible with the cubic symmetry of garnet.
The second ‘star’ precious gem examined was an opaque, black tourmaline of 15.04 ct. Its relatively high refractive indices of 1.625 and 1.646 revealed the black tourmaline must be a stone with relatively high ferrous iron content. The asterism observed in this stone consisted of a six-armed star. The pattern and symmetry of the six arms of the star was homogenous with the trigonal symmetry of tourmaline. However, one additional ‘satellite’ could be observed on one of these arms. It ran from the center of the cabochon alongside the main arm to approximately the middle of the cabochon. A second, less distinct, additional line also ran six main lines. Parallel stripes and scratches could also be observed on the surface of the cabochon; and these were responsible for the synthetic asterism.
At the moment—that is in the stones observed in retail trade up until now, the determination and identification of this kind of manipulation or treatment method to create synthetic asterism has been relatively simple.
A certain number of light lines and/or a symmetry in the star that does not conform to the symmetry of the precious stone itself on which the observed asterism was created synthetically, speaks clearly for manipulation and not for natural asterism. The existence of incomplete arms and light lines with ‘false’ orientation, also known as ‘satellites’ of main arms of the star, also denote that the star was created artificially. The same applies to the parallel scratches that can be observed on the surfaces of the manipulated cabochon under the microscope, if the stones do not have in their centers any ‘needles’ with an orientation and concentration required for the natural creation of a star.
Friday, April 20, 2007
Wednesday, April 18, 2007
Langasite
(via Gemmology Queensland, Vol 3, No.3, March 2002)
Langasite is the name given to a crystal-pulled (Czochralski grown) lanthium gallium silicate. Although designed for use in the communications industry this synthetic material has properties that make it suitable for use as a faceting material.
The material is transparent, dispersive, and of yellow orange to orange color (depending on the oxygen content of the atmosphere in which the crystal is grown).
Langasite has the following identifying properties:
Crystal system: Trigonal
Color: Yellow orange to orange
Hardness: 6 -7
Luster: Vitreous
Diaphaneity: Transparent
Specific gravity: 4.65
Refractive indices: 1.910 – 1.921
Luminescence: Inert
Absorption spectrum: No identifying absorptions
Inclusions: Occasional solid inclusions of triangular shape, rare two phase inclusions.
The only similarly colored gemstone this synthetic is likely to be confused with is zircon (SG=4.70; RI=1.92-1.98). But the characteristic absorption spectrum of zircon (strong line at 653.5nm) should allow effective discrimination between the two.
Langasite is the name given to a crystal-pulled (Czochralski grown) lanthium gallium silicate. Although designed for use in the communications industry this synthetic material has properties that make it suitable for use as a faceting material.
The material is transparent, dispersive, and of yellow orange to orange color (depending on the oxygen content of the atmosphere in which the crystal is grown).
Langasite has the following identifying properties:
Crystal system: Trigonal
Color: Yellow orange to orange
Hardness: 6 -7
Luster: Vitreous
Diaphaneity: Transparent
Specific gravity: 4.65
Refractive indices: 1.910 – 1.921
Luminescence: Inert
Absorption spectrum: No identifying absorptions
Inclusions: Occasional solid inclusions of triangular shape, rare two phase inclusions.
The only similarly colored gemstone this synthetic is likely to be confused with is zircon (SG=4.70; RI=1.92-1.98). But the characteristic absorption spectrum of zircon (strong line at 653.5nm) should allow effective discrimination between the two.
More On Coated Topaz
(via Gemmology Queensland, Vol 3, No.6, July 2002)
Blue, bluish green, and green surface-diffused topaz that are produced in the USA by heat diffusion of a cobalt rich (› blue) or cobalt and nickel rich (› green) powders, have been marketed since 1998. The color, which is uniform to the naked eye, is confined to a thin layer on or jut below the surface of the treated colorless topaz. When examined (immersed) under magnification the diffused layer has a patchy color distribution. Chipped facets reveal underlying colorless topaz. This coating may produce anomalous (› 1.81) reading with the gem refractometer. When examined with the VIS spectroscope, cobalt absorption bands at 560, 590 and 640nm are visible, and this color-enhanced topaz commonly gives a red response when examined with the Chelsea filter.
Well….a new coated topaz has appeared on the market. This treated topaz, that has a brownish ‘imperial’ topaz color was created by Prof Vladimir Balitsky of the Mineralogical Institute, Russian Academy of Sciences. Details of this new treatment were revealed in his recent lecture to The Gemmological Association of All Japan.
The starting material is faceted F-bearing colorless topaz that is coated with a thin layer of iron oxide by heat diffusion. This thin coating gives the topaz a brownish yellow color. When the coating is examined in tangential illumination the facet displays a high, iridescent luster. As the coating is comparatively soft, it is readily abraded and chipped thus exposing the underlying colorless topaz. Refractive indices from the coated facets were 1.61 – 1.62 (normal for F-topaz, including yellow or brown topaz), but the coated topaz did not display the orange LWUV fluorescence normally displayed by imperial (OH-type) topaz.
The Professor remarked that hydrothermally grown synthetic topaz will be soon released on to the world market.
Blue, bluish green, and green surface-diffused topaz that are produced in the USA by heat diffusion of a cobalt rich (› blue) or cobalt and nickel rich (› green) powders, have been marketed since 1998. The color, which is uniform to the naked eye, is confined to a thin layer on or jut below the surface of the treated colorless topaz. When examined (immersed) under magnification the diffused layer has a patchy color distribution. Chipped facets reveal underlying colorless topaz. This coating may produce anomalous (› 1.81) reading with the gem refractometer. When examined with the VIS spectroscope, cobalt absorption bands at 560, 590 and 640nm are visible, and this color-enhanced topaz commonly gives a red response when examined with the Chelsea filter.
Well….a new coated topaz has appeared on the market. This treated topaz, that has a brownish ‘imperial’ topaz color was created by Prof Vladimir Balitsky of the Mineralogical Institute, Russian Academy of Sciences. Details of this new treatment were revealed in his recent lecture to The Gemmological Association of All Japan.
The starting material is faceted F-bearing colorless topaz that is coated with a thin layer of iron oxide by heat diffusion. This thin coating gives the topaz a brownish yellow color. When the coating is examined in tangential illumination the facet displays a high, iridescent luster. As the coating is comparatively soft, it is readily abraded and chipped thus exposing the underlying colorless topaz. Refractive indices from the coated facets were 1.61 – 1.62 (normal for F-topaz, including yellow or brown topaz), but the coated topaz did not display the orange LWUV fluorescence normally displayed by imperial (OH-type) topaz.
The Professor remarked that hydrothermally grown synthetic topaz will be soon released on to the world market.
Chinese Pearl Enhancement Techniques
(Gemmology Queensland, Volume 3, No.6, June 2002)
According to Guo & Shi on pages 32-36 of Volume XXII of The Journal of the Gemmological Association of Hong Kong, Chinese pearl processors apply a range of enhancement technology to both their freshwater and saltwater cultured pearls. These routine treatments include:
- Pre treatment
- Bleaching
- Increasing whiteness
- Adding luster
- Dyeing
- Polishing
Pre Treatment
Pre-treatment process includes sorting, drilling, expansion and dehydration steps. Pearls are sorted on the basis of thickness of nacre, color, luster, shape and size. Drilling allows stringing and setting removes some external defects, and is an essential prerequisite for subsequent treatments for reducing oil content, bleaching, adding whiteness and dyeing pearls. Expansion looses the pearl’s structure and so facilitates future treatment. Two techniques of expansion are used at a temperature of 70-80°C and for times that depend on the depth of color of the pearl (darker color, more time). These techniques of expansion are:
- Heating pearls that have been wrapped in gauze in deionized water.
- Immersion of pearls in an unspecified liquid.
- Dehydration follows expansion. The removal of water from cracks in the pearl is accomplished by immersion in anhydrous ethanol and glycerol.
Bleaching
Bleaching is used to create white pearls and to remove disfiguring colors and stains from the pearls. The common bleaching solution consists of a mixture of hydrogen peroxide, a solvent of surface active reagent (detergent), and a pH stability regulator. Factors affecting the efficiency of bleaching include concentration of hydrogen peroxide, temperature pH of bleaching solution, composition of surface active agent, pH stabilizer and solvent duration of light exposure, and the frequency of stirring and renewal of the bleaching solution.
Two formulations are commonly used for bleaching pearls:
- Hydrogen peroxide carbinol ammonia, 12-alkyl sodium sulphate, Britton-Robinson buffer solvent.
- Hydrogen peroxide chloroform, ethanol amine, 12-alkyl sodium sulphate, Britton-Robinson buffer solvent.
- Common bleaching conditions are a temperature of 30-35°C in association with light exposure. Hydrogen peroxide of 2-3% is commonly used, while bleaching times range from 2-3 days for light colored pearls to more than 10 days for darker colored pearls. The bleaching solution is changed every four days.
Increasing Whiteness
Following bleaching some pearls still retail a yellowish tone due to the presence of pigments resistant to the bleaching effect of hydrogen peroxide. These pearls are further treated with a fluorescent whitener. This is a dye molecule that is activated by the UV in visible light to emit a bluish fluorescence which neutralizes the residual yellow color of pearl and produces a whiter pearl. A Swiss manufactured whitener FP, dissolved in acetone and the surface active agents acrylic acid for 12-alkyl sodium sulphate is the fluorescence whitener commonly used on Chinese pearls.
Adding Luster
This is claimed to be one of the most important processes in pearl enhancement. It involves immersing the pearls in a weakly alkaline TGP (magnesium compounds) solution and keeping them constantly stirred at even temperature for several days.
Dyeing
As bleached pearls usually have some residual uneven color, they are dyed to yield fashionable and marketable colors. Specific dyes are used to produce predictable colors, e.g. potassium permanganate solution with golden NH-R yields golden pearls, while Luo Dan Ming B in alcohol produces pink pearls. These dyes can be either water, oil or alcohol based.
Polishing
Polishing, the last step enhances both the smoothness and luster of the pearls. This step involves surface polishing, usually by tumbling in a mild abrasive, followed by coating of the pearls with a thin layer of wax.
The Problem
- Which of these treatments should be detected?
- Which of these treatments should be disclosed?
According to Guo & Shi on pages 32-36 of Volume XXII of The Journal of the Gemmological Association of Hong Kong, Chinese pearl processors apply a range of enhancement technology to both their freshwater and saltwater cultured pearls. These routine treatments include:
- Pre treatment
- Bleaching
- Increasing whiteness
- Adding luster
- Dyeing
- Polishing
Pre Treatment
Pre-treatment process includes sorting, drilling, expansion and dehydration steps. Pearls are sorted on the basis of thickness of nacre, color, luster, shape and size. Drilling allows stringing and setting removes some external defects, and is an essential prerequisite for subsequent treatments for reducing oil content, bleaching, adding whiteness and dyeing pearls. Expansion looses the pearl’s structure and so facilitates future treatment. Two techniques of expansion are used at a temperature of 70-80°C and for times that depend on the depth of color of the pearl (darker color, more time). These techniques of expansion are:
- Heating pearls that have been wrapped in gauze in deionized water.
- Immersion of pearls in an unspecified liquid.
- Dehydration follows expansion. The removal of water from cracks in the pearl is accomplished by immersion in anhydrous ethanol and glycerol.
Bleaching
Bleaching is used to create white pearls and to remove disfiguring colors and stains from the pearls. The common bleaching solution consists of a mixture of hydrogen peroxide, a solvent of surface active reagent (detergent), and a pH stability regulator. Factors affecting the efficiency of bleaching include concentration of hydrogen peroxide, temperature pH of bleaching solution, composition of surface active agent, pH stabilizer and solvent duration of light exposure, and the frequency of stirring and renewal of the bleaching solution.
Two formulations are commonly used for bleaching pearls:
- Hydrogen peroxide carbinol ammonia, 12-alkyl sodium sulphate, Britton-Robinson buffer solvent.
- Hydrogen peroxide chloroform, ethanol amine, 12-alkyl sodium sulphate, Britton-Robinson buffer solvent.
- Common bleaching conditions are a temperature of 30-35°C in association with light exposure. Hydrogen peroxide of 2-3% is commonly used, while bleaching times range from 2-3 days for light colored pearls to more than 10 days for darker colored pearls. The bleaching solution is changed every four days.
Increasing Whiteness
Following bleaching some pearls still retail a yellowish tone due to the presence of pigments resistant to the bleaching effect of hydrogen peroxide. These pearls are further treated with a fluorescent whitener. This is a dye molecule that is activated by the UV in visible light to emit a bluish fluorescence which neutralizes the residual yellow color of pearl and produces a whiter pearl. A Swiss manufactured whitener FP, dissolved in acetone and the surface active agents acrylic acid for 12-alkyl sodium sulphate is the fluorescence whitener commonly used on Chinese pearls.
Adding Luster
This is claimed to be one of the most important processes in pearl enhancement. It involves immersing the pearls in a weakly alkaline TGP (magnesium compounds) solution and keeping them constantly stirred at even temperature for several days.
Dyeing
As bleached pearls usually have some residual uneven color, they are dyed to yield fashionable and marketable colors. Specific dyes are used to produce predictable colors, e.g. potassium permanganate solution with golden NH-R yields golden pearls, while Luo Dan Ming B in alcohol produces pink pearls. These dyes can be either water, oil or alcohol based.
Polishing
Polishing, the last step enhances both the smoothness and luster of the pearls. This step involves surface polishing, usually by tumbling in a mild abrasive, followed by coating of the pearls with a thin layer of wax.
The Problem
- Which of these treatments should be detected?
- Which of these treatments should be disclosed?
Stanthorpe’s Green Diamond
(via Gemmology Queensland, Volume 3, No.9, September 2002 / The Queensland Government Mining Journal of 15th April, 1924)
A Sad Tale
In a letter to the Brisbane Daily Mail, Mr Oscar Meston (Mining Warden at Stanthorpe) writes:
“On 10th March a cable from London stated that the only known green diamond in existence would be exhibited at the Wembley Exhibition. It weighs a carat and a half, is worth £1750, and was found in the Transvaal in 1923. The Stanthorpe mineral field has produced a rival to this remarkable gem. A few years ago my eye was attracted by ‘coruscation’ from a heap of tailings on an abandoned tin claim. I discovered the source of the light to be a small green stone, which I immediately recognized as a diamond. It was a perfect octahedron, pale green in color, flawless, and a limpid beauty—and it weighed two carats and a half. The surface showed very fine striations, evidently caused by movement under enormous pressure. I offered the stone to several gem merchants in Sydney, but found them almost as adamant as the diamond itself. Their chief objection was the excessive hardness of the Australian diamond and consequent lapidarian difficulties. The utmost I could obtain for the stone was 20 guineas. On the basis of valuation of the Transvaal stone, I lost approximately £2900 on the transaction.”
A Sad Tale
In a letter to the Brisbane Daily Mail, Mr Oscar Meston (Mining Warden at Stanthorpe) writes:
“On 10th March a cable from London stated that the only known green diamond in existence would be exhibited at the Wembley Exhibition. It weighs a carat and a half, is worth £1750, and was found in the Transvaal in 1923. The Stanthorpe mineral field has produced a rival to this remarkable gem. A few years ago my eye was attracted by ‘coruscation’ from a heap of tailings on an abandoned tin claim. I discovered the source of the light to be a small green stone, which I immediately recognized as a diamond. It was a perfect octahedron, pale green in color, flawless, and a limpid beauty—and it weighed two carats and a half. The surface showed very fine striations, evidently caused by movement under enormous pressure. I offered the stone to several gem merchants in Sydney, but found them almost as adamant as the diamond itself. Their chief objection was the excessive hardness of the Australian diamond and consequent lapidarian difficulties. The utmost I could obtain for the stone was 20 guineas. On the basis of valuation of the Transvaal stone, I lost approximately £2900 on the transaction.”
Every One Needs A 10x
(How to) Use it seriously
(via Gemmology Queensland, No.3. No 6, July 2002) Trevor Linton writes:
Carry it all the time and use it as much as possible every day. A 10x lens increases knowledge. A 10x is the first and possibly the most serious instrument used by both the amateur and professional when investigating a gemstone’s features and information as to its origin.
The hand lens, (10x or times—10) is a combination of lenses that provides magnified detail to the observer. It is the most important instrument you can use when an unknown gemstone is given to you either for purchase or for identification. Do not dismiss this step of the investigation into a gemstone during your quest for information, as the hand lens is the only instrument that provides an overall view of a gemstone. The 10x hand lens, in experienced hands, and under quality lighting, can provide essential identification features on 90 percent of gemstones: by noting hardness, refractive index, birefringence, dichroism and dispersion as well as indications of the gemstone’s origin from inclusions and many methods of man’s treatment.
The quality of a 10x hand lens is usually dependant on price, which can vary from A $10 to $320 depending on its type, source, manufacturer and country of origin. There are three main lens combinations that govern the quality of the lens: the plano-convex doublet, the achromatic doublet, and the compound triplet. Each has its advantages and disadvantages.
The first type, the economic doublet has two simple crown glass lenses facing each other at approximately two thirds of their focal length. This combination of lenses provides a 40 percent field of vision that is in reasonable focus and has a relatively flat field. When observing a sheet of squared paper with the doublet, an image appears. This is suitable for rough investigation of stones, but when serious images of a flat facet are required, it leaves a lot to be desired……as straight lines are curved, only the center is in focus as the observed field is curved through a doublet. The colors red and blue are not in focus with green. The advantage for the doublet is economy. A lot of detail can be gathered for a small outlay of dollars with a doublet. Chromatic aberration is usually not a great influence with gemstones as only highlights are refracted in to the differing points of color focus that produce color fringing. Most gemstone observations are in gemstones of one color or colorless gemstones.
Increased color resolution is achieved with a flint glass lens cemented to the inside a double sided convex crown glass lens forming an achromatic compound lens that corrects for the chromatic aberrations that defocus colors in a lens system. This second type of lens system produces straight lines over most of the field of view. An achromatic doublet is a very good, yet still economic 10x system of lenses.
The third lens type, the triplet lens, is a solid system of glass lenses using three layers of glass cemented together forming an aplanatic (in a plane) triplet. The image of a flat plane forms as a plane at the point of focus. This is the best system for hand lenses, when correctly designed and used under normal observation. A triplet has minimal spherical and chromatic aberration and a flat field.
When purchasing a hand lens, buy one that is better than you initially need. If you buy the best triplet lens, use it to your advantage. That s what the whole project should be about. You have to achieve quality observation. There is little advantage in using a quality lens without good lighting and knowledge of how to use both.
When using the hand lens there are several basic rules, and many techniques to develop:
- Spectacles should not be worn unless severe optical defects are present within eyes.
- Choose a good quality light source, with a very narrow beam of high intensity light directed on to your work area and not spilling light towards your eye or the background.
- Work over a soft white cloth that allows easy pick up of gemstones with tweezers. This soft cloth also prevents dropped gemstones from bouncing off the work area on to the floor.
- Clean the sample free from dust and grease (fingerprints) with a lint free cloth. A quality glasses cleaning cloth is suitable.
- Always pick up gemstones with tweezers after cleaning.
- When using the right eye hold the hand lens in the right hand about 25mm in front of the eye, with the index finger primary knuckle resting on the neck.
- Keep both eyes open. This can occur with experience. When the closed eye lid flutters letting light in there is a complimentary iris movement in the open eye.
- Holding the lens close to the eye with one hand, bring the gemstone close with the other hand and rest both hands together for stability. Position the stone 25mm in front of the lens with the gem’s surface in focus, under the light.
- Ensure the lens is straight in front of your eye and is not twisted. Looking off the central axis will produce ‘coma’ color fringing on all images that severely limit quality observing.
- Work systematically around the surface of all faceted gemstones before being drawn into the gems interior. There are many features available for observation, especially around the girdle. Gemstones such as diamond reveal their true nature on the girdle, with natural crystal surfaces left on opposite side of the girdle as the cutters try to achieve maximum weight from the rough stone. The treatment of the girdle or how it was formed is a good guide to the cutting quality and whether care was taken during the gem’s manufacture.
- Do not neglect other features such as flat facets and sharp facet edges that indicate hard gemstones. Concave facets or molding marks at the girdle indicate cast glass. Reflect a fluorescent tube image from the facet for an image of a straight flat facet. Surface luster of facet edges chips indicates the refractive index of the gemstone. Try looking at glass or quartz and comparing surface chips with those on sapphire or diamond. Yes diamond does chip before it cleaves in to two diamonds.
The history of a gemstone’s growth, and subsequent heat and coloring activities induced by man, occurs in the gem’s inclusions. Your 10x hand lens will reveal many of these features under these proposed lighting techniques of use.
Inclusion types have a greater listing than there are gemstone types. Quartz alone has 550 officially listed inclusion types. Quartz is a low temperature forming gemstone; it is of the last to crystallize and includes many other gems that form before it does. Pegmatites in which quartz forms have plenty of liquid and gas so there are many of these inclusions in the ‘veils’ that form within fractures of quartz crystal.
Igneous (volcanic) gemstones can be easily distinguished from metamorphic gems by the individual suites of inclusions within each type. Man-made gems may be chemically identical with those of nature, but man’s techniques of manufacturing these gems create characteristic inclusions that are identifiable with your 10x hand lens.
An interesting feature is found on many older gemstones when a flat plane of air bubbles are glued in a layer between the crown and pavilion of a doublet. These are very easily found with a hand lens. Dispersion of color at individual facets is a good indicator of high refractive index and hardness.
Other hand lenses in use through the industry, such as the Coddington lens and the darkfield loupe have specific features for overcoming specific problems. For example, The Coddington lens is a solid glass cylinder with a restricting light aperture half way at its focal point. This light restriction reduces many aberration errors by preventing them passing the restriction. The darkfield loupe provides correct darkfield lighting for identifying small inclusions in gemstones and direction specific illumination on fracture fill inclusions. This is a small pocket portable, torch based instrument that has power full application in the diamond market of Europe, USA and Asia.
Recommendations
- Use your 10x for it can increase your knowledge and understanding of gemstones.
- A 10x lens is so much faster to use than a microscope that requires more detailed observation. Wear it out as soon as possible and buy a better quality lens as a Christmas present to yourself. If an excuse is needed, it will improve your observing and self-confidence. Do no think that the old 10x will do for the time being.
- Your 10x lens will repay with valuable information.
- Understanding information from a 10x depends on experience gained from informed and correct use f your most important instrument.
(via Gemmology Queensland, No.3. No 6, July 2002) Trevor Linton writes:
Carry it all the time and use it as much as possible every day. A 10x lens increases knowledge. A 10x is the first and possibly the most serious instrument used by both the amateur and professional when investigating a gemstone’s features and information as to its origin.
The hand lens, (10x or times—10) is a combination of lenses that provides magnified detail to the observer. It is the most important instrument you can use when an unknown gemstone is given to you either for purchase or for identification. Do not dismiss this step of the investigation into a gemstone during your quest for information, as the hand lens is the only instrument that provides an overall view of a gemstone. The 10x hand lens, in experienced hands, and under quality lighting, can provide essential identification features on 90 percent of gemstones: by noting hardness, refractive index, birefringence, dichroism and dispersion as well as indications of the gemstone’s origin from inclusions and many methods of man’s treatment.
The quality of a 10x hand lens is usually dependant on price, which can vary from A $10 to $320 depending on its type, source, manufacturer and country of origin. There are three main lens combinations that govern the quality of the lens: the plano-convex doublet, the achromatic doublet, and the compound triplet. Each has its advantages and disadvantages.
The first type, the economic doublet has two simple crown glass lenses facing each other at approximately two thirds of their focal length. This combination of lenses provides a 40 percent field of vision that is in reasonable focus and has a relatively flat field. When observing a sheet of squared paper with the doublet, an image appears. This is suitable for rough investigation of stones, but when serious images of a flat facet are required, it leaves a lot to be desired……as straight lines are curved, only the center is in focus as the observed field is curved through a doublet. The colors red and blue are not in focus with green. The advantage for the doublet is economy. A lot of detail can be gathered for a small outlay of dollars with a doublet. Chromatic aberration is usually not a great influence with gemstones as only highlights are refracted in to the differing points of color focus that produce color fringing. Most gemstone observations are in gemstones of one color or colorless gemstones.
Increased color resolution is achieved with a flint glass lens cemented to the inside a double sided convex crown glass lens forming an achromatic compound lens that corrects for the chromatic aberrations that defocus colors in a lens system. This second type of lens system produces straight lines over most of the field of view. An achromatic doublet is a very good, yet still economic 10x system of lenses.
The third lens type, the triplet lens, is a solid system of glass lenses using three layers of glass cemented together forming an aplanatic (in a plane) triplet. The image of a flat plane forms as a plane at the point of focus. This is the best system for hand lenses, when correctly designed and used under normal observation. A triplet has minimal spherical and chromatic aberration and a flat field.
When purchasing a hand lens, buy one that is better than you initially need. If you buy the best triplet lens, use it to your advantage. That s what the whole project should be about. You have to achieve quality observation. There is little advantage in using a quality lens without good lighting and knowledge of how to use both.
When using the hand lens there are several basic rules, and many techniques to develop:
- Spectacles should not be worn unless severe optical defects are present within eyes.
- Choose a good quality light source, with a very narrow beam of high intensity light directed on to your work area and not spilling light towards your eye or the background.
- Work over a soft white cloth that allows easy pick up of gemstones with tweezers. This soft cloth also prevents dropped gemstones from bouncing off the work area on to the floor.
- Clean the sample free from dust and grease (fingerprints) with a lint free cloth. A quality glasses cleaning cloth is suitable.
- Always pick up gemstones with tweezers after cleaning.
- When using the right eye hold the hand lens in the right hand about 25mm in front of the eye, with the index finger primary knuckle resting on the neck.
- Keep both eyes open. This can occur with experience. When the closed eye lid flutters letting light in there is a complimentary iris movement in the open eye.
- Holding the lens close to the eye with one hand, bring the gemstone close with the other hand and rest both hands together for stability. Position the stone 25mm in front of the lens with the gem’s surface in focus, under the light.
- Ensure the lens is straight in front of your eye and is not twisted. Looking off the central axis will produce ‘coma’ color fringing on all images that severely limit quality observing.
- Work systematically around the surface of all faceted gemstones before being drawn into the gems interior. There are many features available for observation, especially around the girdle. Gemstones such as diamond reveal their true nature on the girdle, with natural crystal surfaces left on opposite side of the girdle as the cutters try to achieve maximum weight from the rough stone. The treatment of the girdle or how it was formed is a good guide to the cutting quality and whether care was taken during the gem’s manufacture.
- Do not neglect other features such as flat facets and sharp facet edges that indicate hard gemstones. Concave facets or molding marks at the girdle indicate cast glass. Reflect a fluorescent tube image from the facet for an image of a straight flat facet. Surface luster of facet edges chips indicates the refractive index of the gemstone. Try looking at glass or quartz and comparing surface chips with those on sapphire or diamond. Yes diamond does chip before it cleaves in to two diamonds.
The history of a gemstone’s growth, and subsequent heat and coloring activities induced by man, occurs in the gem’s inclusions. Your 10x hand lens will reveal many of these features under these proposed lighting techniques of use.
Inclusion types have a greater listing than there are gemstone types. Quartz alone has 550 officially listed inclusion types. Quartz is a low temperature forming gemstone; it is of the last to crystallize and includes many other gems that form before it does. Pegmatites in which quartz forms have plenty of liquid and gas so there are many of these inclusions in the ‘veils’ that form within fractures of quartz crystal.
Igneous (volcanic) gemstones can be easily distinguished from metamorphic gems by the individual suites of inclusions within each type. Man-made gems may be chemically identical with those of nature, but man’s techniques of manufacturing these gems create characteristic inclusions that are identifiable with your 10x hand lens.
An interesting feature is found on many older gemstones when a flat plane of air bubbles are glued in a layer between the crown and pavilion of a doublet. These are very easily found with a hand lens. Dispersion of color at individual facets is a good indicator of high refractive index and hardness.
Other hand lenses in use through the industry, such as the Coddington lens and the darkfield loupe have specific features for overcoming specific problems. For example, The Coddington lens is a solid glass cylinder with a restricting light aperture half way at its focal point. This light restriction reduces many aberration errors by preventing them passing the restriction. The darkfield loupe provides correct darkfield lighting for identifying small inclusions in gemstones and direction specific illumination on fracture fill inclusions. This is a small pocket portable, torch based instrument that has power full application in the diamond market of Europe, USA and Asia.
Recommendations
- Use your 10x for it can increase your knowledge and understanding of gemstones.
- A 10x lens is so much faster to use than a microscope that requires more detailed observation. Wear it out as soon as possible and buy a better quality lens as a Christmas present to yourself. If an excuse is needed, it will improve your observing and self-confidence. Do no think that the old 10x will do for the time being.
- Your 10x lens will repay with valuable information.
- Understanding information from a 10x depends on experience gained from informed and correct use f your most important instrument.
Tuesday, April 17, 2007
Natural Forsterite And Synthetic Forsterite
(via Gemmology Queensland, Vol.4, No.1, January 2003) Hiroshi Kitawaki writes:
Forsterite is one of the end member minerals in the olivine group of minerals. It was named after a British mineral collector Jacob Forster.
Many solid solutions of olivine minerals are known, among which forsterite and fayalite form an isomorphous series. A yellow green crystal, with intermediate composition in this isomorphous series is called peridot. This gemstone is a birthstone of August and is one of the popular gemstones. On the other hand, forsterite is not common a as gemstone.
A forsterite that a chemical formula of, or close to, the end member is rare because one element (Mg) in the formula is generally replaced easily by Fe in nature. The mineral, forsterite, is found in ultrabasic rock or dolomitic limestone that had gone through thermal metamorphism.
Natural Forsterite
The green stone described in this report is a natural forsterite that we recently investigated and it is said to be from Sri Lanka according to its client. Its RI measured 1.635 – 1.670 with DR 0.035. The SG was 3.29 and the stone was inert to UV light. Directionally oriented minute needle-like inclusions were observed under magnification. Its compositional analysis by X-ray fluorescence detected considerable amount of Fe and very small amount of Ca and Mn as well as the main elements of Mg and Si.
Crystals within the olivine group have been extensively studied, and used in heat resistant materials, insulators or lasers. Among the crystals used in industry, single crystal forsterite of high quality and large size have been synthesized by the crystal pulling method for use as crystals that laze the near infrared.
Synthetic forsterite
Synthetic forsterite, which is marketed as Tanzaniod has been synthesized in Russia for gem use. As you can easily imagine from its name, it is meant to imitate tanzanite. The RI, DR and SG of the Tanzaniod are consistent with those of natural forsterite, with Tanzaniod fluorescing a weak orange to yellow and greenish yellow under long and short wave ultraviolet lights respectively. Prominent pleochroism of blue and violet is also recognized. Under the hand-held spectroscope, absorption bands are seen on 490nm, 520nm and 580nm. Dot-like and short needle-like inclusions are observed under magnification. The compositional analysis by fluorescent X-ray detected considerable amount of Co and V, other than the main elements of Mg and Si.
Forsterite is one of the end member minerals in the olivine group of minerals. It was named after a British mineral collector Jacob Forster.
Many solid solutions of olivine minerals are known, among which forsterite and fayalite form an isomorphous series. A yellow green crystal, with intermediate composition in this isomorphous series is called peridot. This gemstone is a birthstone of August and is one of the popular gemstones. On the other hand, forsterite is not common a as gemstone.
A forsterite that a chemical formula of, or close to, the end member is rare because one element (Mg) in the formula is generally replaced easily by Fe in nature. The mineral, forsterite, is found in ultrabasic rock or dolomitic limestone that had gone through thermal metamorphism.
Natural Forsterite
The green stone described in this report is a natural forsterite that we recently investigated and it is said to be from Sri Lanka according to its client. Its RI measured 1.635 – 1.670 with DR 0.035. The SG was 3.29 and the stone was inert to UV light. Directionally oriented minute needle-like inclusions were observed under magnification. Its compositional analysis by X-ray fluorescence detected considerable amount of Fe and very small amount of Ca and Mn as well as the main elements of Mg and Si.
Crystals within the olivine group have been extensively studied, and used in heat resistant materials, insulators or lasers. Among the crystals used in industry, single crystal forsterite of high quality and large size have been synthesized by the crystal pulling method for use as crystals that laze the near infrared.
Synthetic forsterite
Synthetic forsterite, which is marketed as Tanzaniod has been synthesized in Russia for gem use. As you can easily imagine from its name, it is meant to imitate tanzanite. The RI, DR and SG of the Tanzaniod are consistent with those of natural forsterite, with Tanzaniod fluorescing a weak orange to yellow and greenish yellow under long and short wave ultraviolet lights respectively. Prominent pleochroism of blue and violet is also recognized. Under the hand-held spectroscope, absorption bands are seen on 490nm, 520nm and 580nm. Dot-like and short needle-like inclusions are observed under magnification. The compositional analysis by fluorescent X-ray detected considerable amount of Co and V, other than the main elements of Mg and Si.
Natural Hemimorphite And Natural Smithsonite
(via Gemmology Queensland, Vol.4,No.2, February 2003) Hiroshi Kitawaki writes:
We have increasingly encountered natural blue hemimorphite recently. Some of these seem to be easily confused with smithsonite, and this month we are comparing the gemological characteristics of these two stones.
Hemimorphite
The name Hemimorphite was derived from the form of the crystals of this mineral that shows distinct hemimorphism (in which both terminations show different forms). Its Japanese name is Ikyoku-Kou. The mineral is orthorhombic. It is not durable, as its hardness is low at about 4½ to 5 on Mohs scale. However, those hemimorphites with beautiful color, or pronounced transparency, are often cut for jewelry. Colorless, blue, yellow or brown are common, but cabochoned blue stones are more popular these days. The RI of hemimorphite is about 1.61-1.64 with DR 0.022. Its SG is 3.4 to 3.5, and it is inert to UV with no particular feature in the spectrum. Fibrous crystals of hemimorphite characteristically appear striped when examined magnification.
Smithsonite
Smithsonite was named after the mineralogist J Smithson who contributed financially to the establishment of the Smithsonian Institution in Washington, USA. The mineral is named Ryo-Aen-Icou in Japanese, which relates to its chemical composition. Smithsonite is a trigonal mineral, and it is isomorphous with calcite. Although the stone, like hemimorphite, possesses low hardness of 4 to 4½, pose a challenge to its durability. Smithsonites with beautiful colors such as blue, pink, green or yellow will be cabochoned or even faceted. The RI is around 1.62-1.84 and it has a large DR of 0.037. Its SG is 4.3 to 4.5.
When comparing the features of the minerals described above, a SG test will be the most useful way to distinguish them. When use of SG test is restricted due to the presence of setting, elemental analysis or infrared spectral analysis by FTIR will provide you with discriminatory information.
We have increasingly encountered natural blue hemimorphite recently. Some of these seem to be easily confused with smithsonite, and this month we are comparing the gemological characteristics of these two stones.
Hemimorphite
The name Hemimorphite was derived from the form of the crystals of this mineral that shows distinct hemimorphism (in which both terminations show different forms). Its Japanese name is Ikyoku-Kou. The mineral is orthorhombic. It is not durable, as its hardness is low at about 4½ to 5 on Mohs scale. However, those hemimorphites with beautiful color, or pronounced transparency, are often cut for jewelry. Colorless, blue, yellow or brown are common, but cabochoned blue stones are more popular these days. The RI of hemimorphite is about 1.61-1.64 with DR 0.022. Its SG is 3.4 to 3.5, and it is inert to UV with no particular feature in the spectrum. Fibrous crystals of hemimorphite characteristically appear striped when examined magnification.
Smithsonite
Smithsonite was named after the mineralogist J Smithson who contributed financially to the establishment of the Smithsonian Institution in Washington, USA. The mineral is named Ryo-Aen-Icou in Japanese, which relates to its chemical composition. Smithsonite is a trigonal mineral, and it is isomorphous with calcite. Although the stone, like hemimorphite, possesses low hardness of 4 to 4½, pose a challenge to its durability. Smithsonites with beautiful colors such as blue, pink, green or yellow will be cabochoned or even faceted. The RI is around 1.62-1.84 and it has a large DR of 0.037. Its SG is 4.3 to 4.5.
When comparing the features of the minerals described above, a SG test will be the most useful way to distinguish them. When use of SG test is restricted due to the presence of setting, elemental analysis or infrared spectral analysis by FTIR will provide you with discriminatory information.
Natural Hemimorphite And Natural Smithsonite
(via Gemmology Queensland, Vol.4,No.2, February 2003) Hiroshi Kitawaki writes:
We have increasingly encountered natural blue hemimorphite recently. Some of these seem to be easily confused with smithsonite, and this month we are comparing the gemological characteristics of these two stones.
Hemimorphite
The name Hemimorphite was derived from the form of the crystals of this mineral that shows distinct hemimorphism (in which both terminations show different forms). Its Japanese name is Ikyoku-Kou. The mineral is orthorhombic. It is not durable, as its hardness is low at about 4½ to 5 on Mohs scale. However, those hemimorphites with beautiful color, or pronounced transparency, are often cut for jewelry. Colorless, blue, yellow or brown are common, but cabochoned blue stones are more popular these days. The RI of hemimorphite is about 1.61-1.64 with DR 0.022. Its SG is 3.4 to 3.5, and it is inert to UV with no particular feature in the spectrum. Fibrous crystals of hemimorphite characteristically appear striped when examined magnification.
Smithsonite
Smithsonite was named after the mineralogist J Smithson who contributed financially to the establishment of the Smithsonian Institution in Washington, USA. The mineral is named Ryo-Aen-Icou in Japanese, which relates to its chemical composition. Smithsonite is a trigonal mineral, and it is isomorphous with calcite. Although the stone, like hemimorphite, possesses low hardness of 4 to 4½, pose a challenge to its durability. Smithsonites with beautiful colors such as blue, pink, green or yellow will be cabochoned or even faceted. The RI is around 1.62-1.84 and it has a large DR of 0.037. Its SG is 4.3 to 4.5.
When comparing the features of the minerals described above, a SG test will be the most useful way to distinguish them. When use of SG test is restricted due to the presence of setting, elemental analysis or infrared spectral analysis by FTIR will provide you with discriminatory information.
We have increasingly encountered natural blue hemimorphite recently. Some of these seem to be easily confused with smithsonite, and this month we are comparing the gemological characteristics of these two stones.
Hemimorphite
The name Hemimorphite was derived from the form of the crystals of this mineral that shows distinct hemimorphism (in which both terminations show different forms). Its Japanese name is Ikyoku-Kou. The mineral is orthorhombic. It is not durable, as its hardness is low at about 4½ to 5 on Mohs scale. However, those hemimorphites with beautiful color, or pronounced transparency, are often cut for jewelry. Colorless, blue, yellow or brown are common, but cabochoned blue stones are more popular these days. The RI of hemimorphite is about 1.61-1.64 with DR 0.022. Its SG is 3.4 to 3.5, and it is inert to UV with no particular feature in the spectrum. Fibrous crystals of hemimorphite characteristically appear striped when examined magnification.
Smithsonite
Smithsonite was named after the mineralogist J Smithson who contributed financially to the establishment of the Smithsonian Institution in Washington, USA. The mineral is named Ryo-Aen-Icou in Japanese, which relates to its chemical composition. Smithsonite is a trigonal mineral, and it is isomorphous with calcite. Although the stone, like hemimorphite, possesses low hardness of 4 to 4½, pose a challenge to its durability. Smithsonites with beautiful colors such as blue, pink, green or yellow will be cabochoned or even faceted. The RI is around 1.62-1.84 and it has a large DR of 0.037. Its SG is 4.3 to 4.5.
When comparing the features of the minerals described above, a SG test will be the most useful way to distinguish them. When use of SG test is restricted due to the presence of setting, elemental analysis or infrared spectral analysis by FTIR will provide you with discriminatory information.
Fortall™
Jewellery News Asia writes:
This is a new emerald green man-made material that is being marketed through Rough Synthetic Stones Co Ltd (RSS) of Bangkok.
This crystal pulled material has:
- An emerald green color…although the crystals are also available in black, blue, brown, and red colors
- A hardness of 7 on Mohs scale
- A specific gravity of 2.70
- A refractive index (presumably SR) of 1.72
Before being marketed as a jewelry accessory, this material has been used for industrial purposes. Fortall™ is available both as rough and as faceted stones.
This is a new emerald green man-made material that is being marketed through Rough Synthetic Stones Co Ltd (RSS) of Bangkok.
This crystal pulled material has:
- An emerald green color…although the crystals are also available in black, blue, brown, and red colors
- A hardness of 7 on Mohs scale
- A specific gravity of 2.70
- A refractive index (presumably SR) of 1.72
Before being marketed as a jewelry accessory, this material has been used for industrial purposes. Fortall™ is available both as rough and as faceted stones.
Created Turquoise & Coral
Sanwa Pearl Trading are marketing look-alike imitation of turquoise and coral that are being produced in Germany ‘under high pressure and temperature by a special bonding agent and contain no epoxy resin.’
Branded Cubic Zirconia
Machine cut faceted CZ that displays the ‘hearts & arrows’ effect is being marketed as Hsini Star™ cubic zirconia.
Be on the look out for:
- CZ that displays an alexandrite effect when viewed in different light sources.
- Brown CZ that imitates brown diamond.
- Black CZ that does not change color when submitted to high temperature.
Be on the look out for:
- CZ that displays an alexandrite effect when viewed in different light sources.
- Brown CZ that imitates brown diamond.
- Black CZ that does not change color when submitted to high temperature.
Monday, April 16, 2007
Pyrite vs Marcasite
(via Gemmology Queensland, Vol.4, No.7, July 2003)
The marcasites of jewelry are a misnomer, for the brassy colored flattened pyramids and rose cuts, that were hand set or cemented into mid-18th century and Victorian jewelry, were manufactured from pyrite…not marcasite. Marcasite’s lack of chemical stability makes this mineral useless for jewelry purposes.
The word pyrite is derived from the Greek root pyros = fire, thus alluding to the sparks generated when this mineral is struck by steel. The origin of the word marcasite is less certain but is likely derived from the Latin word marcasita.
Although, chemically pyrite and marcasite are dimorphs of the mineral iron sulphide (FeS), their properties are quite different.
Pyrite
Crystal system: cubic
Habit: interpenetrant cubes; modified pyritohedra
Color: brassy yellow
Hardness: 6-6½
Fracture: conchoidal; uneven
Specific gravity: 5
Luster: metallic
Diaphaneity: opaque
Streak: greenish black
Identifying features: brassy with greenish black streak
Marcasite
Crystal system: orthorhombic
Habit: spear-shaped twins; cocks-comb aggregates
Color: brassy yellow
Hardness: 6-6½
Fracture: uneven
Specific gravity: 4.8-4.9
Luster: metallic
Diaphaneity: opaque
Streak: grayish brownish black
Identifying features: evidence of surface degredation (powdering)
Presently marcasite (pyrite) set jewelry is rapidly coming back into vogue as inexpensive surface decoration for jewelry and watches. Most of the newer marcasites are being manufactured in China, and are glued into silver or silver plated copper settings; their cutting and polishing into pointed square shapes must be accurate.
A Tip
When checking marcasite-set jewelry for quality, ensure:
- each marcasite is of uniform size and thickness.
- polished surfaces are free of surface pits.
- the marcasites display a uniform brassy metallic luster in reflected light.
The marcasites of jewelry are a misnomer, for the brassy colored flattened pyramids and rose cuts, that were hand set or cemented into mid-18th century and Victorian jewelry, were manufactured from pyrite…not marcasite. Marcasite’s lack of chemical stability makes this mineral useless for jewelry purposes.
The word pyrite is derived from the Greek root pyros = fire, thus alluding to the sparks generated when this mineral is struck by steel. The origin of the word marcasite is less certain but is likely derived from the Latin word marcasita.
Although, chemically pyrite and marcasite are dimorphs of the mineral iron sulphide (FeS), their properties are quite different.
Pyrite
Crystal system: cubic
Habit: interpenetrant cubes; modified pyritohedra
Color: brassy yellow
Hardness: 6-6½
Fracture: conchoidal; uneven
Specific gravity: 5
Luster: metallic
Diaphaneity: opaque
Streak: greenish black
Identifying features: brassy with greenish black streak
Marcasite
Crystal system: orthorhombic
Habit: spear-shaped twins; cocks-comb aggregates
Color: brassy yellow
Hardness: 6-6½
Fracture: uneven
Specific gravity: 4.8-4.9
Luster: metallic
Diaphaneity: opaque
Streak: grayish brownish black
Identifying features: evidence of surface degredation (powdering)
Presently marcasite (pyrite) set jewelry is rapidly coming back into vogue as inexpensive surface decoration for jewelry and watches. Most of the newer marcasites are being manufactured in China, and are glued into silver or silver plated copper settings; their cutting and polishing into pointed square shapes must be accurate.
A Tip
When checking marcasite-set jewelry for quality, ensure:
- each marcasite is of uniform size and thickness.
- polished surfaces are free of surface pits.
- the marcasites display a uniform brassy metallic luster in reflected light.
Another Use For Lapis Lazuli
(via Gemmology Queensland, Vol.4, No.9, September 200 / From the Precious Lapis Lazuli gemstone)
Lapis lazuli pigment was once only attainable in small quantities. Recent advancements in refining technology has made it possible to produce a pure natural lapis pigment (ultramarine blue) of consistent high quality in commercial quantities.
The pigment originates from the Chilean lapis lazuli deposit owned by Las Flores de los andes S.A and located high in the Chilean Andes in the province of Coquimbo. It is produced in Chile by Lapis Pigments S.A with technical advice from European scientists.
The pure royal blue pigment, also known as natural ultramarine blue, is extracted from the gemstone. Lapis lazuli has a history of more than five thousand years as jewelry, ornamental art and as a pigment. The great masters of the Renaissance period immortalized the blue ultramarine pigment in their famous works. The value of the pigment then exceeded the price of gold.
The natural lapis lazuli pigment differentiates itself from this synthetic counterpart by the vibrancy of the blue that it produces. The natural pigment particles, large in size, have an irregular and angular shape. With their multiple surfaces this natural pigment reacts to light like a finely faceted diamond, thereby producing an ever-changing display of rich vibrant blues. This creates a three-dimensional, gem-like effect that is not attainable with the very small, round and uniformly shaped particles of the synthetic ultramarine blue pigment.
The natural lapis lazuli is suitable for use in paints, lacquers, inks and cosmetics. It is successfully being used in the coating of metallic and other surfaces.
Lapis lazuli pigment was once only attainable in small quantities. Recent advancements in refining technology has made it possible to produce a pure natural lapis pigment (ultramarine blue) of consistent high quality in commercial quantities.
The pigment originates from the Chilean lapis lazuli deposit owned by Las Flores de los andes S.A and located high in the Chilean Andes in the province of Coquimbo. It is produced in Chile by Lapis Pigments S.A with technical advice from European scientists.
The pure royal blue pigment, also known as natural ultramarine blue, is extracted from the gemstone. Lapis lazuli has a history of more than five thousand years as jewelry, ornamental art and as a pigment. The great masters of the Renaissance period immortalized the blue ultramarine pigment in their famous works. The value of the pigment then exceeded the price of gold.
The natural lapis lazuli pigment differentiates itself from this synthetic counterpart by the vibrancy of the blue that it produces. The natural pigment particles, large in size, have an irregular and angular shape. With their multiple surfaces this natural pigment reacts to light like a finely faceted diamond, thereby producing an ever-changing display of rich vibrant blues. This creates a three-dimensional, gem-like effect that is not attainable with the very small, round and uniformly shaped particles of the synthetic ultramarine blue pigment.
The natural lapis lazuli is suitable for use in paints, lacquers, inks and cosmetics. It is successfully being used in the coating of metallic and other surfaces.
Colored Gemstone Grading…..Friend or Foe?
(via Rapaport Diamond Report, Vol.30, No.9, March 2, 2007) Antoinette Matlins writes:
“If you walk around the AGTA show, you do not see many AGTA grading reports. Who is getting these reports? It is not the dealers, but often the consumers. They invest in the stones and send them to grading labs to verify what the dealers have told them. The colored gemstone dealers in this industry are not educated. They often represent material as natural and not heated when, in fact, the goods are heated. Dealers don’t understand the science of gemology but simply tell their clients whatever they have been told. The dealers know they have been making money this way, so why change? The trade in general has not accepted its responsibilities to the final client and most do not provide proper documentation. I have offered to provide gemological services and educational seminars free of charge to AGTA members. They never call me.”
“If you walk around the AGTA show, you do not see many AGTA grading reports. Who is getting these reports? It is not the dealers, but often the consumers. They invest in the stones and send them to grading labs to verify what the dealers have told them. The colored gemstone dealers in this industry are not educated. They often represent material as natural and not heated when, in fact, the goods are heated. Dealers don’t understand the science of gemology but simply tell their clients whatever they have been told. The dealers know they have been making money this way, so why change? The trade in general has not accepted its responsibilities to the final client and most do not provide proper documentation. I have offered to provide gemological services and educational seminars free of charge to AGTA members. They never call me.”
NDT Solution
Non-destructive Testing for Identifying Natural, Synthetic, Treated, and Imitation Gem Materials
(via Gemmology Queensland, Volume 4, No.9, September 2003) Taijin Lu and James E Shigley writes:
In the daily business of NDT, it is easy to lose sight of the wide range of applications for NDT techniques. In this month’s featured article, the authors have outlined the application of NDT techniques in evaluating natural and synthetic gems. It is always interesting to see in what new ways NDT is used, and how it helps diverse industries or endeavors—G.P.Singh, Associate Technical Editor, The American Society For NonDestructive Testing.
Introduction
Accurate identification is essential to maintain the commercial value of gemstones. It is also required to enable jewelers to disclose to their customers the correct identity of the gemstones they sell. In identifying and studying fashioned gemstones, any testing must be performed nondestructively without altering the gemstones shape or appearance. When presented for testing, some gemstones are mounted in jewelry, which can further complicate the testing procedure. By using standard gem testing instruments and techniques, trained gemologists can recognize most gem materials. In some instances, however, they may not be able to distinguish certain synthetic and laboratory treated gem materials, which can have almost the same visual appearance and gemological properties as their natural counterparts. Use of advanced nondestructive imaging, spectroscopic, and chemical analysis techniques helps establish criteria to distinguish gem materials. Several examples are presented of nondestructive testing techniques currently used in gemology.
Gems include a wide range of materials (natural, synthetic, treated, and imitation diamonds, colored stones, and pearls). This requires gathering observations and measurements to determine distinctive characteristics of gem materials. Such characteristics are summarized in standard reference books (Webster, 1994; Liddicoat, 1981).
With the continued development of crystal growth technology, various synthetic and imitation gem materials are increasingly encountered in the jewelry industry (Nassau, 1980; Nassau, 1983, Gubelin and Koivula, 1986; Nassau et al., 1997). For example, synthetic cubic zirconia, and synthetic moissanite (SiC-6H) have a very similar appearance to diamonds, and are used as imitation diamonds. Some of these synthetic materials, such as synthetic ruby, sapphire and emerald, can be grown by several growth techniques (hydrothermal, flux, melt).
Various processes (such as irradiation, heating, filling of open fractures or cavities, and coating) are also used to treat low quality gem materials to improve their color, appearance, or durability (Moses et al., 1999; Johnson et al., 1999; McClure et al., 1999, Reinitz et al., 2000, Nassau, 1983). Typical examples of heat treated gemstones include sapphire (corundum) and citrine (quartz). Irradiation with gamma rays, X-rays, electrons, or neutrons is used to alter the color of specimens of diamond, topaz, and quartz. Both diamonds and emeralds can have surface reaching openings filled with various substances to improve their clarity.
Since synthetic and treated gem materials are regularly seen today in the jewelry market, it is important for gemologists to be able to identify them. Although effective in many cases, traditional gem testing instruments and methods cannot always distinguish synthetic and laboratory treated gem materials from their natural counterparts. Advanced nondestructive characterization techniques enable the gemologist to find diagnostic properties to distinguish these materials. The goal of the gem research program at the Gemological Institute of America is to find relatively practical methods and/or instruments to identify gemstones based on the differences revealed by both standard and advanced nondestructive characterization. Systematic documentation of the gemological properties of various gem materials of known origin, carried out by similar research institutions and others, is also necessary to develop gem identification criteria.
In this article, characterization methods commonly used today in gemology are briefly reviewed, and examples of several methods to identify gem materials are discussed.
Nondestructive methods of gem identification
A number of instruments have been developed over the years to assist the jeweler and gemologist in the identification of gem materials. These instruments are mainly used for evaluating the appearance of gemstones. Visual characteristics such a color, luster, growth features, and inclusions are examined with a 10x magnifier (loupe) and a binocular microscope with bright and dark field illumination and polarizing functions. Refractive index and birefringence (double refraction) are determined by a refractometer. Pleochroism (dichroism) is examined with a dichroscope. Strains and optical character are observed using a polariscope. Visible absorption spectrum is examined with a hand spectroscope. Specific gravity, electric conductivity, and thermal conductivity are measured by a hydrostatic balance, conductivity meter, and thermal conductivity tester respectively. Trained gemologists are familiar with this equipment (Webster, 1994; Liddicoat, 1981).
Advanced methods
The physical and compositional differences between natural, synthetic, and treated gem materials can range from significant to minor. Thus, it is necessary to check for potentially small differences through advanced analytical methods which have sufficiently high resolution and sensitivity. To achieve better resolution and sensitivity, minor modifications had to be made to some of these instruments. These include the design of special sample holders for faceted and/or mounted gem samples, and optimizing the illumination conditions by use of, for example, an optical fiber system for microscopy and spectroscopy. Special accessories such as liquid nitrogen cryogenic unit are also used to record visible absorption spectra of diamonds at low temperature.
Use of the techniques, together with published information, allows the systematic gathering of a database of information on the gem materials to support the developments of practical gem identification criteria.
Application
In the past, a number of low cost natural minerals and man made materials have been used as imitations of colorless diamond. Since these materials differ compositionally from diamond, they have significant differences in one or more of their physical properties, which allow them to be distinguished. The most widespread diamond imitation material today is cubic zirconia (cubic zirconium oxide). Because diamond’s thermal conductivity is superior to that of imitations, jewelers can quickly distinguish diamonds from cubic zirconia and other previously used imitation materials (synthetic corundum, synthetic spinel, zircon, synthetic rutile, strontium titanate, yttrium aluminum garnet, and gadolium gallium garnet) by use of a simple thermal conductivity meter.
Within the past two years, anew near colorless diamond imitation, synthetic moissanite (SiC-6H), has been marketed for jewelry purposes. The thermal conductivity of synthetic moissanite is quite close to that of diamond, so much so that is can be mistakenly identified as diamond using a conventional thermal probe. However, it is optically anisotropic, which causes the junctions between adjacent polished facets to appear doubled when looking through a fashioned piece with a 10x magnifier or a binocular microscope. The refractive appearance of natural diamonds, on the other hand, always includes clearly single junctions between facets. Synthetic moissanite also exhibits electrical conductivity, and has quite different visible, infrared, and Raman spectra from that of diamonds (Nassau, 1983).
Some natural diamonds possess open, surface reaching cleavages which reflect light, and thus make a fashioned diamond look less attractive. During the past decade, a process has been developed to inject a high refractive index, glass-like material into these cleavages to lessen their visibility. Diamond treated in this way can be recognized by the distinctive visual appearance of the filled cracks that can be seen with 10x magnification. Confirmation of this conclusion can be obtained by X-ray radiography, where the photographic image reveals the filled crack. Chemical analysis can detect the presence of high atomic weight elements such as lead or bismuth, which are components of the glass-like filler material used to increase the refractive index (Koivula et al, 1989; Kammerling et al, 1994).
Coloration can be produced in diamond by exposing them to a source of radiation. This coloration can be modified by subsequent heat treatment. In some cases, irradiation treatment gives rise to unusual color zoning or ultraviolet fluorescence, which can help the gemologist identify a color treated diamond. However, distinguishing colored diamonds irradiated in the laboratory (versus the very rare green to blue diamonds irradiated in nature) normally requires recording visible absorption spectra (with the diamond cooled to low temperatures with cryogenic unit), as well as infrared spectra. In some cases, the distinction cannot be made between the exposure of a diamond to a source of radiation in nature or the laboratory. Recently, several companies have begun using high pressure and high temperature processes to treat the color and other characteristics of a select group of natural diamonds. Conclusive identification of these treated color diamonds requires infrared and low temperature visible spectroscopy as well as Raman spectroscopy, but a number of gemological properties provide some indication of HPHT treatment (Moses et al., 1999; Fisher and Spits, 2000); Reinitz et al, 2000).
Synthetic diamond can be grown from a molten metal alloy at high temperatures and pressures by the temperature gradient. The resulting crystals exhibit a cuboctahedral shape (Sunagawa, 1995). Distinctive color zoning, growth features, and metallic inclusions in polished synthetic diamonds can all be observed with a binocular microscope (Shigley et al., 1995). An ultraviolet fluorescence imaging system, known as the DiamondView and developed by De Beers researchers, allows the observation of the fluorescence zoning pattern that is characteristic of synthetic diamonds (Welbourn, 1996). Chemical analysis can reveal the presence of the transition metals (such as iron, nickel, and cobalt) from which the synthetic diamonds grew.
Natural pearls are relatively rare, but are still encountered in jewelry pieces. Most pearls sold today are cultured pearls. They are produced by introducing a mother-of-pearl bead and piece of mantle tissue into the oyster. The oyster is then cultivated under controlled conditions for periods of up to one year or more during which the bead is covered by nacre. In contrast, pearl imitations are usually wax-filled glass, solid glass, plastic, and mother-of-pearl (Liddicoat, 1981; Webster, 1994).
X-radiography is the best method to identify pearls. X-ray absorption images of pearls are recorded on photographic film to reveal the differing internal structures (Liddicoat, 1981; Matlins, 1995; Scarratt et al., 2000). On a radiograph, natural pearls usually show concentric rings outward from the center. Cultured pearls show a clear interface between nacre layer and the bead nucleus, while pearl imitations lack internal structure.
Cultured pearls can be colored by chemical treatments or irradiation. They may also possess a surface coating. Such treatments can often be detected by careful examination with a binocular microscope; chemical analysis may also reveal the presence of a foreign material.
Jade is a polycrystalline gem material consisting of a mixture of silicate minerals. There are two types of jade, one consisting mainly of jadeite (a pyroxene), and the other of nephrite (an amphibole). There are also other green-colored rocks that have been sold as jade, as well as imitations. Since there are a large number of grain boundaries and/or fractures in jade, several treatment processes are used to improve appearance. The most commonly used processes involve chemical bleaching of the original jade to remove brownish stains, and then impregnating it with polymers or other substances to fill surface reaching fractures (Fritsch et al., 1992; Ou Yang, 1997). In some cases, colored dyes are also used to improve the color.
A number of identification criteria for treated jade have been found, such as the peculiarities evident under magnified observation, lower specific gravity, and distinctive infrared spectra. When observed under magnification, it is often possible to see differences in texture or structure that are evidence of treatment. Since the specific gravity of untreated jade is around 3.3 to 3.5, polymer impregnated samples will float in a 3.2 specific gravity liquid because of their lighter specific gravity, whereas untreated jade will sink. Infrared absorption spectra show clear differences between natural and treated jadeite.
Ruby (corundum) is not only one of the best known colored gemstones, but it is also an important optical crystal for industrial uses. It can be synthesized by many methods, such as from a melt by the Czochralski technique, from a flux solution, and recently from a hydrothermal solution (Lu and Shigley, 1998). Synthetic ruby can often be distinguished gemologically by the observation of inclusions, color zoning, and growth features (Liddicoat, 1981; Hughes, 1997, Lu and Shigley, 1998).
When such visual characteristics are not present or cannot be seen, natural and synthetic rubies can be identified on the basis of their trace element chemistry as determined by the energy dispersive X-ray fluorescence method (Muhlmeister et al.,1998). Trace elements such as nickel, molybdenum, lanthanum, tungsten, platinum, lead, or bismuth may be detected in synthetic ruby, as a result of growth in a laboratory environment. The relative proportions of the transition metals chromium, iron, vanadium, and titanium also varies between natural and synthetic rubies, and can be used to distinguish between them.
Amethyst (quartz) is the most important gem variety of quartz, and is found in many localities worldwide. Its synthetic counterpart, grown from either alkaline or fluoride solutions, is produced in Russia, Japan, China, and other countries. The appearance and physical properties of both are very similar.
Based on our study of both natural and synthetic amethyst, we have found that there are characteristic differences in crystal morphology, twinning, inclusions, growth zoning, color banding, infrared spectra, and trace element chemistry. As noted by Lu and Sunagawa (1990), natural amethyst is usually twinned, it exhibits tiny solid inclusions, and it lacks a characteristic infrared absorption band at 2.8mm (1x10¯4 in). Synthetic amethyst grown from fluoride solution displays an unusual growth structure (a stream-like structure), color bands that parallel the seed crystal, distinct infrared spectra, and fluorine and lithium as trace elements. The synthetic amethyst grown from alkaline solution is characterized by growth sectors, color zoning, and distinct infrared spectra.
Emerald (beryl) is the final example of gem identification to be discussed here. Synthetic emerald can be grown from flux and hydrothermal solutions, and it exhibits a number of gemological properties (like synthetic ruby) by which it can be identified.
Many natural emerald crystals often contain surface reaching fractures, due to their growth conditions or perhaps to damage suffered during mining. The presence of these fractures results in an unattractive appearance. Increasingly over the past two decades, a variety of liquid substances (oils, epoxies, resins, etc.) have been used to fill these open fractures, and thus to improve emerald appearance (Kammerling et al, 1991; Johnson et al., 1999). Questions concerning the long term stability of these substances have led to the need not only to determine if an emerald has been treated in this way, but to determine the identity of the filler substance as well. The use of both infrared and Raman spectroscopies has provided new information on the detection of treated emeralds (Johnson et al., 1999).
Discussion and summary
Gem materials consist of a wide range of materials. Most of them are single crystals, usually faceted and polished (and sometimes mounted in jewelry). To support the commercial value of gemstones and the stability of the jewelry market, accurate gem identification is important. The traditional and advanced nondestructive characterization techniques used today for gem identification are based on the distinctive gemological properties of natural, synthetic, treated and imitation gem materials.
Traditional gemological methods and instruments are inexpensive and relatively easy to use. When used by a trained gemologist, they can help to identify most gem materials. In some cases, advanced analytical techniques with higher resolution and sensitivity are required to reveal the small differences in properties among natural, synthetic, and treated gem materials. Advanced techniques can also help identify the geological environment and growth conditions in which a gem material formed. They can also occasionally provide evidence on the geographic origin, which is important for high value natural colored stones such as ruby or sapphire. Although a combination of both the traditional and advanced methods helps to determine the diagnostic properties of gem materials, the development of new, relatively simple and inexpensive testing instruments for use by jewelers remains a challenge. The continued production of new synthetic and treated gem materials requires an equal effort to support practical gem identification to safeguard the jewelry industry.
(via Gemmology Queensland, Volume 4, No.9, September 2003) Taijin Lu and James E Shigley writes:
In the daily business of NDT, it is easy to lose sight of the wide range of applications for NDT techniques. In this month’s featured article, the authors have outlined the application of NDT techniques in evaluating natural and synthetic gems. It is always interesting to see in what new ways NDT is used, and how it helps diverse industries or endeavors—G.P.Singh, Associate Technical Editor, The American Society For NonDestructive Testing.
Introduction
Accurate identification is essential to maintain the commercial value of gemstones. It is also required to enable jewelers to disclose to their customers the correct identity of the gemstones they sell. In identifying and studying fashioned gemstones, any testing must be performed nondestructively without altering the gemstones shape or appearance. When presented for testing, some gemstones are mounted in jewelry, which can further complicate the testing procedure. By using standard gem testing instruments and techniques, trained gemologists can recognize most gem materials. In some instances, however, they may not be able to distinguish certain synthetic and laboratory treated gem materials, which can have almost the same visual appearance and gemological properties as their natural counterparts. Use of advanced nondestructive imaging, spectroscopic, and chemical analysis techniques helps establish criteria to distinguish gem materials. Several examples are presented of nondestructive testing techniques currently used in gemology.
Gems include a wide range of materials (natural, synthetic, treated, and imitation diamonds, colored stones, and pearls). This requires gathering observations and measurements to determine distinctive characteristics of gem materials. Such characteristics are summarized in standard reference books (Webster, 1994; Liddicoat, 1981).
With the continued development of crystal growth technology, various synthetic and imitation gem materials are increasingly encountered in the jewelry industry (Nassau, 1980; Nassau, 1983, Gubelin and Koivula, 1986; Nassau et al., 1997). For example, synthetic cubic zirconia, and synthetic moissanite (SiC-6H) have a very similar appearance to diamonds, and are used as imitation diamonds. Some of these synthetic materials, such as synthetic ruby, sapphire and emerald, can be grown by several growth techniques (hydrothermal, flux, melt).
Various processes (such as irradiation, heating, filling of open fractures or cavities, and coating) are also used to treat low quality gem materials to improve their color, appearance, or durability (Moses et al., 1999; Johnson et al., 1999; McClure et al., 1999, Reinitz et al., 2000, Nassau, 1983). Typical examples of heat treated gemstones include sapphire (corundum) and citrine (quartz). Irradiation with gamma rays, X-rays, electrons, or neutrons is used to alter the color of specimens of diamond, topaz, and quartz. Both diamonds and emeralds can have surface reaching openings filled with various substances to improve their clarity.
Since synthetic and treated gem materials are regularly seen today in the jewelry market, it is important for gemologists to be able to identify them. Although effective in many cases, traditional gem testing instruments and methods cannot always distinguish synthetic and laboratory treated gem materials from their natural counterparts. Advanced nondestructive characterization techniques enable the gemologist to find diagnostic properties to distinguish these materials. The goal of the gem research program at the Gemological Institute of America is to find relatively practical methods and/or instruments to identify gemstones based on the differences revealed by both standard and advanced nondestructive characterization. Systematic documentation of the gemological properties of various gem materials of known origin, carried out by similar research institutions and others, is also necessary to develop gem identification criteria.
In this article, characterization methods commonly used today in gemology are briefly reviewed, and examples of several methods to identify gem materials are discussed.
Nondestructive methods of gem identification
A number of instruments have been developed over the years to assist the jeweler and gemologist in the identification of gem materials. These instruments are mainly used for evaluating the appearance of gemstones. Visual characteristics such a color, luster, growth features, and inclusions are examined with a 10x magnifier (loupe) and a binocular microscope with bright and dark field illumination and polarizing functions. Refractive index and birefringence (double refraction) are determined by a refractometer. Pleochroism (dichroism) is examined with a dichroscope. Strains and optical character are observed using a polariscope. Visible absorption spectrum is examined with a hand spectroscope. Specific gravity, electric conductivity, and thermal conductivity are measured by a hydrostatic balance, conductivity meter, and thermal conductivity tester respectively. Trained gemologists are familiar with this equipment (Webster, 1994; Liddicoat, 1981).
Advanced methods
The physical and compositional differences between natural, synthetic, and treated gem materials can range from significant to minor. Thus, it is necessary to check for potentially small differences through advanced analytical methods which have sufficiently high resolution and sensitivity. To achieve better resolution and sensitivity, minor modifications had to be made to some of these instruments. These include the design of special sample holders for faceted and/or mounted gem samples, and optimizing the illumination conditions by use of, for example, an optical fiber system for microscopy and spectroscopy. Special accessories such as liquid nitrogen cryogenic unit are also used to record visible absorption spectra of diamonds at low temperature.
Use of the techniques, together with published information, allows the systematic gathering of a database of information on the gem materials to support the developments of practical gem identification criteria.
Application
In the past, a number of low cost natural minerals and man made materials have been used as imitations of colorless diamond. Since these materials differ compositionally from diamond, they have significant differences in one or more of their physical properties, which allow them to be distinguished. The most widespread diamond imitation material today is cubic zirconia (cubic zirconium oxide). Because diamond’s thermal conductivity is superior to that of imitations, jewelers can quickly distinguish diamonds from cubic zirconia and other previously used imitation materials (synthetic corundum, synthetic spinel, zircon, synthetic rutile, strontium titanate, yttrium aluminum garnet, and gadolium gallium garnet) by use of a simple thermal conductivity meter.
Within the past two years, anew near colorless diamond imitation, synthetic moissanite (SiC-6H), has been marketed for jewelry purposes. The thermal conductivity of synthetic moissanite is quite close to that of diamond, so much so that is can be mistakenly identified as diamond using a conventional thermal probe. However, it is optically anisotropic, which causes the junctions between adjacent polished facets to appear doubled when looking through a fashioned piece with a 10x magnifier or a binocular microscope. The refractive appearance of natural diamonds, on the other hand, always includes clearly single junctions between facets. Synthetic moissanite also exhibits electrical conductivity, and has quite different visible, infrared, and Raman spectra from that of diamonds (Nassau, 1983).
Some natural diamonds possess open, surface reaching cleavages which reflect light, and thus make a fashioned diamond look less attractive. During the past decade, a process has been developed to inject a high refractive index, glass-like material into these cleavages to lessen their visibility. Diamond treated in this way can be recognized by the distinctive visual appearance of the filled cracks that can be seen with 10x magnification. Confirmation of this conclusion can be obtained by X-ray radiography, where the photographic image reveals the filled crack. Chemical analysis can detect the presence of high atomic weight elements such as lead or bismuth, which are components of the glass-like filler material used to increase the refractive index (Koivula et al, 1989; Kammerling et al, 1994).
Coloration can be produced in diamond by exposing them to a source of radiation. This coloration can be modified by subsequent heat treatment. In some cases, irradiation treatment gives rise to unusual color zoning or ultraviolet fluorescence, which can help the gemologist identify a color treated diamond. However, distinguishing colored diamonds irradiated in the laboratory (versus the very rare green to blue diamonds irradiated in nature) normally requires recording visible absorption spectra (with the diamond cooled to low temperatures with cryogenic unit), as well as infrared spectra. In some cases, the distinction cannot be made between the exposure of a diamond to a source of radiation in nature or the laboratory. Recently, several companies have begun using high pressure and high temperature processes to treat the color and other characteristics of a select group of natural diamonds. Conclusive identification of these treated color diamonds requires infrared and low temperature visible spectroscopy as well as Raman spectroscopy, but a number of gemological properties provide some indication of HPHT treatment (Moses et al., 1999; Fisher and Spits, 2000); Reinitz et al, 2000).
Synthetic diamond can be grown from a molten metal alloy at high temperatures and pressures by the temperature gradient. The resulting crystals exhibit a cuboctahedral shape (Sunagawa, 1995). Distinctive color zoning, growth features, and metallic inclusions in polished synthetic diamonds can all be observed with a binocular microscope (Shigley et al., 1995). An ultraviolet fluorescence imaging system, known as the DiamondView and developed by De Beers researchers, allows the observation of the fluorescence zoning pattern that is characteristic of synthetic diamonds (Welbourn, 1996). Chemical analysis can reveal the presence of the transition metals (such as iron, nickel, and cobalt) from which the synthetic diamonds grew.
Natural pearls are relatively rare, but are still encountered in jewelry pieces. Most pearls sold today are cultured pearls. They are produced by introducing a mother-of-pearl bead and piece of mantle tissue into the oyster. The oyster is then cultivated under controlled conditions for periods of up to one year or more during which the bead is covered by nacre. In contrast, pearl imitations are usually wax-filled glass, solid glass, plastic, and mother-of-pearl (Liddicoat, 1981; Webster, 1994).
X-radiography is the best method to identify pearls. X-ray absorption images of pearls are recorded on photographic film to reveal the differing internal structures (Liddicoat, 1981; Matlins, 1995; Scarratt et al., 2000). On a radiograph, natural pearls usually show concentric rings outward from the center. Cultured pearls show a clear interface between nacre layer and the bead nucleus, while pearl imitations lack internal structure.
Cultured pearls can be colored by chemical treatments or irradiation. They may also possess a surface coating. Such treatments can often be detected by careful examination with a binocular microscope; chemical analysis may also reveal the presence of a foreign material.
Jade is a polycrystalline gem material consisting of a mixture of silicate minerals. There are two types of jade, one consisting mainly of jadeite (a pyroxene), and the other of nephrite (an amphibole). There are also other green-colored rocks that have been sold as jade, as well as imitations. Since there are a large number of grain boundaries and/or fractures in jade, several treatment processes are used to improve appearance. The most commonly used processes involve chemical bleaching of the original jade to remove brownish stains, and then impregnating it with polymers or other substances to fill surface reaching fractures (Fritsch et al., 1992; Ou Yang, 1997). In some cases, colored dyes are also used to improve the color.
A number of identification criteria for treated jade have been found, such as the peculiarities evident under magnified observation, lower specific gravity, and distinctive infrared spectra. When observed under magnification, it is often possible to see differences in texture or structure that are evidence of treatment. Since the specific gravity of untreated jade is around 3.3 to 3.5, polymer impregnated samples will float in a 3.2 specific gravity liquid because of their lighter specific gravity, whereas untreated jade will sink. Infrared absorption spectra show clear differences between natural and treated jadeite.
Ruby (corundum) is not only one of the best known colored gemstones, but it is also an important optical crystal for industrial uses. It can be synthesized by many methods, such as from a melt by the Czochralski technique, from a flux solution, and recently from a hydrothermal solution (Lu and Shigley, 1998). Synthetic ruby can often be distinguished gemologically by the observation of inclusions, color zoning, and growth features (Liddicoat, 1981; Hughes, 1997, Lu and Shigley, 1998).
When such visual characteristics are not present or cannot be seen, natural and synthetic rubies can be identified on the basis of their trace element chemistry as determined by the energy dispersive X-ray fluorescence method (Muhlmeister et al.,1998). Trace elements such as nickel, molybdenum, lanthanum, tungsten, platinum, lead, or bismuth may be detected in synthetic ruby, as a result of growth in a laboratory environment. The relative proportions of the transition metals chromium, iron, vanadium, and titanium also varies between natural and synthetic rubies, and can be used to distinguish between them.
Amethyst (quartz) is the most important gem variety of quartz, and is found in many localities worldwide. Its synthetic counterpart, grown from either alkaline or fluoride solutions, is produced in Russia, Japan, China, and other countries. The appearance and physical properties of both are very similar.
Based on our study of both natural and synthetic amethyst, we have found that there are characteristic differences in crystal morphology, twinning, inclusions, growth zoning, color banding, infrared spectra, and trace element chemistry. As noted by Lu and Sunagawa (1990), natural amethyst is usually twinned, it exhibits tiny solid inclusions, and it lacks a characteristic infrared absorption band at 2.8mm (1x10¯4 in). Synthetic amethyst grown from fluoride solution displays an unusual growth structure (a stream-like structure), color bands that parallel the seed crystal, distinct infrared spectra, and fluorine and lithium as trace elements. The synthetic amethyst grown from alkaline solution is characterized by growth sectors, color zoning, and distinct infrared spectra.
Emerald (beryl) is the final example of gem identification to be discussed here. Synthetic emerald can be grown from flux and hydrothermal solutions, and it exhibits a number of gemological properties (like synthetic ruby) by which it can be identified.
Many natural emerald crystals often contain surface reaching fractures, due to their growth conditions or perhaps to damage suffered during mining. The presence of these fractures results in an unattractive appearance. Increasingly over the past two decades, a variety of liquid substances (oils, epoxies, resins, etc.) have been used to fill these open fractures, and thus to improve emerald appearance (Kammerling et al, 1991; Johnson et al., 1999). Questions concerning the long term stability of these substances have led to the need not only to determine if an emerald has been treated in this way, but to determine the identity of the filler substance as well. The use of both infrared and Raman spectroscopies has provided new information on the detection of treated emeralds (Johnson et al., 1999).
Discussion and summary
Gem materials consist of a wide range of materials. Most of them are single crystals, usually faceted and polished (and sometimes mounted in jewelry). To support the commercial value of gemstones and the stability of the jewelry market, accurate gem identification is important. The traditional and advanced nondestructive characterization techniques used today for gem identification are based on the distinctive gemological properties of natural, synthetic, treated and imitation gem materials.
Traditional gemological methods and instruments are inexpensive and relatively easy to use. When used by a trained gemologist, they can help to identify most gem materials. In some cases, advanced analytical techniques with higher resolution and sensitivity are required to reveal the small differences in properties among natural, synthetic, and treated gem materials. Advanced techniques can also help identify the geological environment and growth conditions in which a gem material formed. They can also occasionally provide evidence on the geographic origin, which is important for high value natural colored stones such as ruby or sapphire. Although a combination of both the traditional and advanced methods helps to determine the diagnostic properties of gem materials, the development of new, relatively simple and inexpensive testing instruments for use by jewelers remains a challenge. The continued production of new synthetic and treated gem materials requires an equal effort to support practical gem identification to safeguard the jewelry industry.
Saturday, April 14, 2007
Innovative Color Enhancement
(via Gem Scoup) Simon Bruce Lockhart writes:
Like any county, and particularly like those who population sometimes sees a disproportionate amount of disadvantaged civilians, Sri Lanka enjoys its fair share of friendly, open, and utterly charming confidence tricksters. Innovative local ‘color enhancement techniques’ are employed on yellow and blue sapphires to obtain high prices. The wily rascals of Elahera roll rough sapphires around in simple carbon paper. The deep blue carbon rubs off on the rough gem yielding an ‘improved’ coloration, which exhibits top cornflower blues worth a fortune. However this trick can literally come apart in your hands as the blue carbon rubs off the gem and onto your fingers.
Another ‘color enhancement’ trick unique to Sri Lanka enhances yellow sapphires by use of a well-known indigenous tree called the ‘Goraka Tree’. Known for possessing a saffron-yellow resin, a hole is gouged into the soft three trunk and a less than honest dealer presses a pale sapphire into the tree, leaving it there for several days. After wiping clean, the whole gem is stained a rich and vivid yellow color that is extremely convincing—until cut. While practices such as these are deplorable, one can’t help being impressed with the ingenuity of these somewhat creative conmen.
Like any county, and particularly like those who population sometimes sees a disproportionate amount of disadvantaged civilians, Sri Lanka enjoys its fair share of friendly, open, and utterly charming confidence tricksters. Innovative local ‘color enhancement techniques’ are employed on yellow and blue sapphires to obtain high prices. The wily rascals of Elahera roll rough sapphires around in simple carbon paper. The deep blue carbon rubs off on the rough gem yielding an ‘improved’ coloration, which exhibits top cornflower blues worth a fortune. However this trick can literally come apart in your hands as the blue carbon rubs off the gem and onto your fingers.
Another ‘color enhancement’ trick unique to Sri Lanka enhances yellow sapphires by use of a well-known indigenous tree called the ‘Goraka Tree’. Known for possessing a saffron-yellow resin, a hole is gouged into the soft three trunk and a less than honest dealer presses a pale sapphire into the tree, leaving it there for several days. After wiping clean, the whole gem is stained a rich and vivid yellow color that is extremely convincing—until cut. While practices such as these are deplorable, one can’t help being impressed with the ingenuity of these somewhat creative conmen.
Ruby From The Vatomandry Area Of Eastern Madagascar
(via Gemmology Queensland, Vol.5, No.3, March 2004)
For about a year, Thai gem merchants have been selling considerable amounts of ruby from a recently discovered alluvial source in central eastern Madagascar. The principal source of this ruby is an area about 15km south-west of the central coastal town of Vatomandry. Ruby from this deposit has several interesting features:
- A considerable proportion of the rough does not require heat treatment.
- Some of the ruby closely resembles premium Burmese ruby in color.
In the recently published July 2001 issue of The Journal of Gemmology (pp 409-416), Schwartz & Schemetzer have described the identifying features of this ruby. The authors research has revealed that although ruby from this deposit displays the conventional properties of ruby, their fluorescence was weak to medium for LWUV and inert to very weak for SWUV (due to their 0.1-0.7 wt% content of Fe³+).
Characteristic inclusions observed in specimens that had not been treated included:
- Twin lamellae oriented in two directions.
- Intersecting twin lamellae decorated by tube to needle-like masses of white boehmite particles.
- Short needles and twinned or elongated plate-like crystals of rutile that are oriented in three directions.
- No visible growth zoning.
- Clusters of small, colorless to whitish birefringent zircon crystals.
- A few large apatite crystals.
- Healed fractures of variable shapes.
Trace element analysis of Vatomandry ruby revealed that this ruby has a higher (0.1-0.7 wt%) iron content than Burmese ruby (0.005 wt%), and it contains more vanadium (0.005-0.07 wt %) that Thai-Cambodian ruby (0.01 wt%).
Further, the authors suggest that heat treatment of this ruby at low temperature (<1450°C) to remove any purplish overtone could be difficult to detect—particularly if the rubies only had rutile and clusters of zircon as their only inclusions.
The authors conclude that this ruby’s unique trace element chemistry, combined with its lack of growth zoning, short rutile needles, and clusters of small zircon, will allow its discrimination from ruby of similar color but differing provenance such as Burma and Thailand-Cambodia.
For about a year, Thai gem merchants have been selling considerable amounts of ruby from a recently discovered alluvial source in central eastern Madagascar. The principal source of this ruby is an area about 15km south-west of the central coastal town of Vatomandry. Ruby from this deposit has several interesting features:
- A considerable proportion of the rough does not require heat treatment.
- Some of the ruby closely resembles premium Burmese ruby in color.
In the recently published July 2001 issue of The Journal of Gemmology (pp 409-416), Schwartz & Schemetzer have described the identifying features of this ruby. The authors research has revealed that although ruby from this deposit displays the conventional properties of ruby, their fluorescence was weak to medium for LWUV and inert to very weak for SWUV (due to their 0.1-0.7 wt% content of Fe³+).
Characteristic inclusions observed in specimens that had not been treated included:
- Twin lamellae oriented in two directions.
- Intersecting twin lamellae decorated by tube to needle-like masses of white boehmite particles.
- Short needles and twinned or elongated plate-like crystals of rutile that are oriented in three directions.
- No visible growth zoning.
- Clusters of small, colorless to whitish birefringent zircon crystals.
- A few large apatite crystals.
- Healed fractures of variable shapes.
Trace element analysis of Vatomandry ruby revealed that this ruby has a higher (0.1-0.7 wt%) iron content than Burmese ruby (0.005 wt%), and it contains more vanadium (0.005-0.07 wt %) that Thai-Cambodian ruby (0.01 wt%).
Further, the authors suggest that heat treatment of this ruby at low temperature (<1450°C) to remove any purplish overtone could be difficult to detect—particularly if the rubies only had rutile and clusters of zircon as their only inclusions.
The authors conclude that this ruby’s unique trace element chemistry, combined with its lack of growth zoning, short rutile needles, and clusters of small zircon, will allow its discrimination from ruby of similar color but differing provenance such as Burma and Thailand-Cambodia.
Where Did Spectacles Come From?
(via Gemmology Queensland, Vol.4, No.11, November 2003 / IIS Newsletter 80/2003)
Apparently no visual instruments existed at the time of the ancient Egyptians, Greeks, or Romans. At least this view is supported by a letter written by a prominent Roman about 100 B.C in which he stressed his resignation to old age and his complaint that he could no longer read for himself, having instead to rely on his slaves. The Roman tragedian Seneca, born in about 4 B.C is alleged to have read all the books in Rome by peering at them through a glass globe of water to produce magnification. Nero used an emerald held up to his eye while he watched gladiators fight. This is not proof that the Romans had any idea about lenses, since it is likely that Nero used the emerald because of its green color, which filtered the sunlight. Ptolemy mentions the general principle of magnification; but the lenses then available were unsuitable for use in precise magnification.
The oldest known lens was found in the ruins of ancient Nineveh and was made of polished rock crystal, an inch and one-half in diameter. Aristophanes in ‘The Clouds’ refers to a glass for burning holes in parchment and also mentions the use of burning glasses for erasing writing from wax tablets. According to Pliny, physicians used them for cauterizing wounds. Around 1000 A.D the reading stone, what we know as a magnifying glass, was developed. It was a segment of a glass sphere that could be laid against reading material to magnify the letters. It enables presbyopic (short sighted) monks to read and was probably the first reading aid.
The Venetians learned how to produce glass for reading ‘stones’, and later they constructed lenses that could be held in a frame in front of the eyes instead of directly on the reading material. Spectacles as we know them, were invented some 700 hundred years ago, presumably in Northern Italy. The oldest complete specimens date from sometime around 1350 and were found in the excavation of a nunnery near Celle in Germany. The first glasses were made out of beryl, a semi-precious stone, from which glasses obtained their name in Germanic languages, where they are called bril or brille.
The first known artistic representation of eyeglasses was painted by Tommaso da Modena in 1352. He did a series of frescoes of brothers busily reading or copying manuscripts. One holds a magnifying glass, but another has glasses perched on his nose. Once Tommaso had established the precedent, other painters placed spectacles on the noses of all sorts of subjects, probably as a symbol of wisdom and respect.
The first spectacles had quartz lenses because optical glass had not been developed. The lenses were set into bone, metal or even leather mountings, often shaped like two small magnifying glasses with handles riveted together typically in an inverted V shape that could be balanced on the bridge of the nose. The use of spectacles spread from Italy to the Low Countries, Germany, Spain, and France. In England, a Spectacle Makers Company was formed in 1629; its coat of arms showed three pairs of spectacles and a motto: ‘A blessing to the aged’.
Benjamin Franklin in the 1780’s developed the bifocal. Later he wrote, “I therefore had formerly two pairs of spectacles, which I shifted occasionally, as in traveling I sometimes read, and often wanted to regard the prospects. Finding this change troublesome, and not always sufficiently ready, I had the glasses cut and a half of each kind associated in the same circle. By this means, as I wear my own spectacles constantly, I have only to move my eyes by or down, as I want to see distinctly far or near, the proper glasses being always ready.” Modern eyeglass frames can be made of almost any material, including ivory, tortoiseshell, wood, metal, and plastic.
Apparently no visual instruments existed at the time of the ancient Egyptians, Greeks, or Romans. At least this view is supported by a letter written by a prominent Roman about 100 B.C in which he stressed his resignation to old age and his complaint that he could no longer read for himself, having instead to rely on his slaves. The Roman tragedian Seneca, born in about 4 B.C is alleged to have read all the books in Rome by peering at them through a glass globe of water to produce magnification. Nero used an emerald held up to his eye while he watched gladiators fight. This is not proof that the Romans had any idea about lenses, since it is likely that Nero used the emerald because of its green color, which filtered the sunlight. Ptolemy mentions the general principle of magnification; but the lenses then available were unsuitable for use in precise magnification.
The oldest known lens was found in the ruins of ancient Nineveh and was made of polished rock crystal, an inch and one-half in diameter. Aristophanes in ‘The Clouds’ refers to a glass for burning holes in parchment and also mentions the use of burning glasses for erasing writing from wax tablets. According to Pliny, physicians used them for cauterizing wounds. Around 1000 A.D the reading stone, what we know as a magnifying glass, was developed. It was a segment of a glass sphere that could be laid against reading material to magnify the letters. It enables presbyopic (short sighted) monks to read and was probably the first reading aid.
The Venetians learned how to produce glass for reading ‘stones’, and later they constructed lenses that could be held in a frame in front of the eyes instead of directly on the reading material. Spectacles as we know them, were invented some 700 hundred years ago, presumably in Northern Italy. The oldest complete specimens date from sometime around 1350 and were found in the excavation of a nunnery near Celle in Germany. The first glasses were made out of beryl, a semi-precious stone, from which glasses obtained their name in Germanic languages, where they are called bril or brille.
The first known artistic representation of eyeglasses was painted by Tommaso da Modena in 1352. He did a series of frescoes of brothers busily reading or copying manuscripts. One holds a magnifying glass, but another has glasses perched on his nose. Once Tommaso had established the precedent, other painters placed spectacles on the noses of all sorts of subjects, probably as a symbol of wisdom and respect.
The first spectacles had quartz lenses because optical glass had not been developed. The lenses were set into bone, metal or even leather mountings, often shaped like two small magnifying glasses with handles riveted together typically in an inverted V shape that could be balanced on the bridge of the nose. The use of spectacles spread from Italy to the Low Countries, Germany, Spain, and France. In England, a Spectacle Makers Company was formed in 1629; its coat of arms showed three pairs of spectacles and a motto: ‘A blessing to the aged’.
Benjamin Franklin in the 1780’s developed the bifocal. Later he wrote, “I therefore had formerly two pairs of spectacles, which I shifted occasionally, as in traveling I sometimes read, and often wanted to regard the prospects. Finding this change troublesome, and not always sufficiently ready, I had the glasses cut and a half of each kind associated in the same circle. By this means, as I wear my own spectacles constantly, I have only to move my eyes by or down, as I want to see distinctly far or near, the proper glasses being always ready.” Modern eyeglass frames can be made of almost any material, including ivory, tortoiseshell, wood, metal, and plastic.
Administratium
(via Gemmology Queensland, Vol.5, No.6, June 2004) Steve Sorrell writes:
The heaviest element known to science was recently discovered. The element, tentatively named Administratium , has no protons or electrons and thus has an atomic number 0. However, it does have 1 neutron, 125 assistant neutrons, 75 vice neutrons and 111 assistant vice neutrons, giving it an atomic mass of 312. These 312 particles are held together in the nucleus by a force that involves the continuous exchange of meson-like particles called morons.
Since it has no electrons, Administratium is inert. However, it can be detected chemically as it impedes every reaction with which it comes in contact. According to the discoverers, a tiny amount of Administratium caused one reaction to take over 4 days to complete when it would normally occur in less than one second.
Administratium has a normal half-life of approximately 3 years. At this time it doesn’t actually decay but instead undergoes reorganization in which assistant neutrons, vice neutrons, and assistant vice neutrons exchange places. Some studies have shown that the atomic mass actually increased after each reorganization.
Researchers at other laboratories indicated that Administratium occurs naturally in the atmosphere. It tends to concentrate at certain points such as universities, government agencies, large corporations, and schools. The element can be found in the newest, best-appointed and best-maintained buildings.
Scientists point out that Administratium is known to be toxic at any level of concentration and can easily destroy any productive reactions where it is allowed to accumulate. Attempts are being made to determine how Administratium can be controlled to prevent irreversible damage, but results are not promising.
The heaviest element known to science was recently discovered. The element, tentatively named Administratium , has no protons or electrons and thus has an atomic number 0. However, it does have 1 neutron, 125 assistant neutrons, 75 vice neutrons and 111 assistant vice neutrons, giving it an atomic mass of 312. These 312 particles are held together in the nucleus by a force that involves the continuous exchange of meson-like particles called morons.
Since it has no electrons, Administratium is inert. However, it can be detected chemically as it impedes every reaction with which it comes in contact. According to the discoverers, a tiny amount of Administratium caused one reaction to take over 4 days to complete when it would normally occur in less than one second.
Administratium has a normal half-life of approximately 3 years. At this time it doesn’t actually decay but instead undergoes reorganization in which assistant neutrons, vice neutrons, and assistant vice neutrons exchange places. Some studies have shown that the atomic mass actually increased after each reorganization.
Researchers at other laboratories indicated that Administratium occurs naturally in the atmosphere. It tends to concentrate at certain points such as universities, government agencies, large corporations, and schools. The element can be found in the newest, best-appointed and best-maintained buildings.
Scientists point out that Administratium is known to be toxic at any level of concentration and can easily destroy any productive reactions where it is allowed to accumulate. Attempts are being made to determine how Administratium can be controlled to prevent irreversible damage, but results are not promising.
The Monkey Puzzle Tree: Claimed Source Of Jet
(via Gemmology Queensland, Vol.5, No.6, June 2004)
The araucaria family (Araucariaceae) contains three remarkable genera of cone-bearing trees: Araucaria, Agathis, and Wollemia. They are tall trees native to forested regions of South America and Australia. In majestic size and beauty, they certainly rival the coniferous forests of North America and Eurasia. In fact, they are considered the southern counterpart of our northern pine forests. The type genus Araucaria is derived from ‘Arauco’, a region in central Chile where the Araucani Indians live. This is also the land of the ‘monkey puzzle’ tree (A. araucana), so named because the prickly, tangled branches would be difficult for a monkey to climb. Fossil evidence indicates that ancestral araucaria forests resembling the present day monkey puzzle date back to the age of dinosaurs. In fact, it has been suggested the tree’s armor of dagger-like leaves was designed to discourage enormous South American herbivorous dinosaurs, such as Argentinosaurus weighing and estimated 80 to 100 tons. Another ancient South American species called pino parana or parana pine (A. angustifolia) grows in southern Brazil and Argentina.
Any discussion of fossilized araucariads would be incomplete without mentioning a medieval gemstone called jet. Jet is a semi-precious gem excavated in Europe and formed by metamorphosis and anaerobic fossilization of araucaria wood buried under sediments in ancient seas. Ancestral forests that metamorphosed into jet date back to the Jurassic period, about 160 million years ago. They were similar to present day forests of monkey puzzle trees (Araucaria araucana) that grow in South America. Chemically, jet is hard, carbonized form of bituminous coal with a density similar to anthracite coal. Anthracite can be readily identified by its metallic luster. Jet takes a high polish and has been used for shiny black jewelry for thousands of years. It has a specific gravity of 1.3, almost as hard as the ironwood called lignum vitae (Guaiacum officinale). Jet became very popular during the mid 19th century England during the reign of Queen Victoria, and was often worn to ward off evil spirits and during times of mourning. In the first century AD, the Roman naturalist and writer Pliny described the magical and medicinal attributes of this beautiful mineral. The well-known analogy of ‘jet’ and ‘black’ was coined by William Shakespeare in his ‘black as jet’ from Henry VI part 2. One of the most famous areas for mining of Victorian jet is Whitby on the rugged Northeast coast of England. Although they are similar in hardness, anthracite has a metallic luster and jet is dull black. Jet takes a high polish and has been used in various carved jewelry, such as cameos and intaglios. The Victoria jet broach (circa 1890) was a popular item of jewelry during the 19th century.
The araucaria family (Araucariaceae) contains three remarkable genera of cone-bearing trees: Araucaria, Agathis, and Wollemia. They are tall trees native to forested regions of South America and Australia. In majestic size and beauty, they certainly rival the coniferous forests of North America and Eurasia. In fact, they are considered the southern counterpart of our northern pine forests. The type genus Araucaria is derived from ‘Arauco’, a region in central Chile where the Araucani Indians live. This is also the land of the ‘monkey puzzle’ tree (A. araucana), so named because the prickly, tangled branches would be difficult for a monkey to climb. Fossil evidence indicates that ancestral araucaria forests resembling the present day monkey puzzle date back to the age of dinosaurs. In fact, it has been suggested the tree’s armor of dagger-like leaves was designed to discourage enormous South American herbivorous dinosaurs, such as Argentinosaurus weighing and estimated 80 to 100 tons. Another ancient South American species called pino parana or parana pine (A. angustifolia) grows in southern Brazil and Argentina.
Any discussion of fossilized araucariads would be incomplete without mentioning a medieval gemstone called jet. Jet is a semi-precious gem excavated in Europe and formed by metamorphosis and anaerobic fossilization of araucaria wood buried under sediments in ancient seas. Ancestral forests that metamorphosed into jet date back to the Jurassic period, about 160 million years ago. They were similar to present day forests of monkey puzzle trees (Araucaria araucana) that grow in South America. Chemically, jet is hard, carbonized form of bituminous coal with a density similar to anthracite coal. Anthracite can be readily identified by its metallic luster. Jet takes a high polish and has been used for shiny black jewelry for thousands of years. It has a specific gravity of 1.3, almost as hard as the ironwood called lignum vitae (Guaiacum officinale). Jet became very popular during the mid 19th century England during the reign of Queen Victoria, and was often worn to ward off evil spirits and during times of mourning. In the first century AD, the Roman naturalist and writer Pliny described the magical and medicinal attributes of this beautiful mineral. The well-known analogy of ‘jet’ and ‘black’ was coined by William Shakespeare in his ‘black as jet’ from Henry VI part 2. One of the most famous areas for mining of Victorian jet is Whitby on the rugged Northeast coast of England. Although they are similar in hardness, anthracite has a metallic luster and jet is dull black. Jet takes a high polish and has been used in various carved jewelry, such as cameos and intaglios. The Victoria jet broach (circa 1890) was a popular item of jewelry during the 19th century.
Rare Diamond Goes Bright Pink In UV Light
(via Gemmology Queensland, Vol.5, No.7, July 2004/annanova.com 16/1/04)
A potentially unique diamond, which goes vivid pink when exposed to ultraviolet light, has been found in South Africa. The 13.7 carat diamond, being called the Tirisano Easter Diamond, was recovered from the Tirisano Diamond Mine in Ventersdorp diamond district of the Republic of South Africa.
Exposure to (presumably long wave) ultraviolet light causes the diamond to turn vibrant fluorescent pink. It’s not unusual for diamonds to change color in this way, but vivid pink is one of the rarest colors and the stone retains this hue for a period of time after UV exposure. Experts who have examined it so far consider it to be unique but the exact rarity of the stone will have to be established by a laboratory.
It is the property of mining companies Etruscan and Mountain Lake who plan to sell it by auction to a private collector. Les Meyer, a director of National Diamond Marketing, said, “I have had cause to view several million of stones but I have never come across a diamond of this nature, which leads me to believe that it is incredibly rare. It’s an exceptional piece due to the vibrant pink fluorescence and it has caused excitement amongst all who have examined it at National Diamond Marketing. Nobody can quite believe the color transition.”
A potentially unique diamond, which goes vivid pink when exposed to ultraviolet light, has been found in South Africa. The 13.7 carat diamond, being called the Tirisano Easter Diamond, was recovered from the Tirisano Diamond Mine in Ventersdorp diamond district of the Republic of South Africa.
Exposure to (presumably long wave) ultraviolet light causes the diamond to turn vibrant fluorescent pink. It’s not unusual for diamonds to change color in this way, but vivid pink is one of the rarest colors and the stone retains this hue for a period of time after UV exposure. Experts who have examined it so far consider it to be unique but the exact rarity of the stone will have to be established by a laboratory.
It is the property of mining companies Etruscan and Mountain Lake who plan to sell it by auction to a private collector. Les Meyer, a director of National Diamond Marketing, said, “I have had cause to view several million of stones but I have never come across a diamond of this nature, which leads me to believe that it is incredibly rare. It’s an exceptional piece due to the vibrant pink fluorescence and it has caused excitement amongst all who have examined it at National Diamond Marketing. Nobody can quite believe the color transition.”
Thursday, April 12, 2007
Crystal-pulled Synthetic Chrysoberyl
(via Gemmology Queensland, Vol.1, No.2, February 2000)
According to Dr Hisashi Machida, of Japan’s Kyocera Corporation, Inamori currently produces twelve (12) synthetics for gem purposes. These man-made materials include flux-grown emerald, flocculated silica based plastic impregnated white and black opal, and synthetic alexandrite, cat’s eye alexandrite, blue sapphire, ruby, star ruby, pink sapphire, yellow sapphire, padparadscha sapphire, and green chrysoberyl which Machida claims are synthesized by a combination of a flux process and pulling.
Japan’s Kyocera Corporation has been producing gem quality Czochralski grown (crystal pulled) synthetic chrysoberyl for many years. While yellow (Fe³+ bearing), colorless, and Cr³+ containing alexandrite chrysoberyls have been available for some years, green and pink chrysoberyl have only recently been added to the product list.
The light green colored synthetic chrysoberyl is virtually inclusion-free, and is colored by V³+ of similar concentration to that found in Tunduru chrysoberyl of comparable color. Detectable quantities of Fe, Ga, and Sn were not found in the Inamori crystal-pulled synthetic chrysoberyl.
A bluish green synthetic chrysoberyl of possible Russian origin, was colored by five times the V³+ found in equivalently colored natural chrysoberyl, about 0.2 wt% Cr2O3. Like the Inamori synthetic, this green synthetic chrysoberyl had no detectable Fe, Ga, Sn.
An experimental pink synthetic chrysoberyl was colored by Ti³+ (the same chromophore that is found in hydrothermally grown pink synthetic beryl. This synthetic also was virtually inclusion free.
According to Dr Hisashi Machida, of Japan’s Kyocera Corporation, Inamori currently produces twelve (12) synthetics for gem purposes. These man-made materials include flux-grown emerald, flocculated silica based plastic impregnated white and black opal, and synthetic alexandrite, cat’s eye alexandrite, blue sapphire, ruby, star ruby, pink sapphire, yellow sapphire, padparadscha sapphire, and green chrysoberyl which Machida claims are synthesized by a combination of a flux process and pulling.
Japan’s Kyocera Corporation has been producing gem quality Czochralski grown (crystal pulled) synthetic chrysoberyl for many years. While yellow (Fe³+ bearing), colorless, and Cr³+ containing alexandrite chrysoberyls have been available for some years, green and pink chrysoberyl have only recently been added to the product list.
The light green colored synthetic chrysoberyl is virtually inclusion-free, and is colored by V³+ of similar concentration to that found in Tunduru chrysoberyl of comparable color. Detectable quantities of Fe, Ga, and Sn were not found in the Inamori crystal-pulled synthetic chrysoberyl.
A bluish green synthetic chrysoberyl of possible Russian origin, was colored by five times the V³+ found in equivalently colored natural chrysoberyl, about 0.2 wt% Cr2O3. Like the Inamori synthetic, this green synthetic chrysoberyl had no detectable Fe, Ga, Sn.
An experimental pink synthetic chrysoberyl was colored by Ti³+ (the same chromophore that is found in hydrothermally grown pink synthetic beryl. This synthetic also was virtually inclusion free.
Wednesday, April 11, 2007
Identifying Synthetic Moissanite
(via Gems & Jewellery News, December 1998) Jamie Nelson writes:
If a large batch of unmounted diamonds of a range of sizes requires to be checked to determine if the batch has been salted with synthetic moissanites, then there is an easy alternative method to the methylene iodide sink or float separations.
Place the stones, table down, on the bottom of a shallow, flat bottomed, clear glass dish and cover all the stones completely with tap water. The much higher optical dispersion of moissanite (0.104 or almost x 2½ that of diamond) will reveal itself as bright spectral colored flashes, while diamonds (dispersion 0.044) will display less brightly colored sparkles. The method will still work with open-backed bracelets, necklaces and other items provided that all the stones lie table down (i.e. culet uppermost).
This being so, in the case of a finger ring mounted moissanite, the only piece of equipment needed to ensure a confident distinction is a battery-operated hand-held polariscope. The ring is placed between the polars so that the place of the stone’s table lies parallel to the optic axis of the polariscope, i.e. the long torch battery stem. The polariscope is then rotated in the axis of the torch barrel while keeping the ring stationary.
If the stone is moissanite, the usual winking of the stone’s image will be seen. If it is diamond, little or no change in the scattered light intensity will be observed. If the colorless stone happens to be another uniaxial or biaxial material, such as zircon, rutile, lithium niobate, corundum, scheelite, zincite, topaz or enstatite, then of course winking effects also will be seen. But all will be unable to pass a scratch-hardness test using the sharp edge of a carborundum (alpha silicon carbide) monocrystal applied cautiously to the girdle. However, our concern here is only to disclose the presence of moissanite and not to identify a nondiamond stone.
If a large batch of unmounted diamonds of a range of sizes requires to be checked to determine if the batch has been salted with synthetic moissanites, then there is an easy alternative method to the methylene iodide sink or float separations.
Place the stones, table down, on the bottom of a shallow, flat bottomed, clear glass dish and cover all the stones completely with tap water. The much higher optical dispersion of moissanite (0.104 or almost x 2½ that of diamond) will reveal itself as bright spectral colored flashes, while diamonds (dispersion 0.044) will display less brightly colored sparkles. The method will still work with open-backed bracelets, necklaces and other items provided that all the stones lie table down (i.e. culet uppermost).
This being so, in the case of a finger ring mounted moissanite, the only piece of equipment needed to ensure a confident distinction is a battery-operated hand-held polariscope. The ring is placed between the polars so that the place of the stone’s table lies parallel to the optic axis of the polariscope, i.e. the long torch battery stem. The polariscope is then rotated in the axis of the torch barrel while keeping the ring stationary.
If the stone is moissanite, the usual winking of the stone’s image will be seen. If it is diamond, little or no change in the scattered light intensity will be observed. If the colorless stone happens to be another uniaxial or biaxial material, such as zircon, rutile, lithium niobate, corundum, scheelite, zincite, topaz or enstatite, then of course winking effects also will be seen. But all will be unable to pass a scratch-hardness test using the sharp edge of a carborundum (alpha silicon carbide) monocrystal applied cautiously to the girdle. However, our concern here is only to disclose the presence of moissanite and not to identify a nondiamond stone.
Synthetic Aquamarine
(via Gemmology Queensland, Vol.1, No.2, February 2000)
Tairus first produced light to dark greenish blue synthetic aquamarine in Russia in the mid-1990s. It is synthesized hydrothermally, and owes its greenish color to small amounts of Fe²+ and a Fe²+ - Fe³+ charge transfer mechanism. It is grown as flat tabular crystals on seed plates oriented at an angle to the c-axis.
Hyrothermally grown synthetic aquamarine has the following gemological properties:
Color: Light to dark greenish blue
Specific gravity: 2.65 – 2.70
Refractive index: 1.587/1.580 – 1.571/1.577
Birefringence: 0.004/0.008
Pleochroism: Weak to strong blue/colorless
Fluorescence (UV): Inert
VIS absorption spectrum: Bands at 800nm (Fe²+ ), 375nm ( Fe³+ ), shoulder at 650nm (Fe²+ - Fe³+ charge transfer, line at 400nm (Ni³+)
It can be discriminated from natural aquamarine by its:
- Chevron-like growth banding that parallels the seed plate. This growth banding which is made up of pyramidal sub-cellular growth subunits is typical of hydrothermal growth occurring of seed plates oriented at an angle to its c-axis.
- Occasional presence of flake-like aggregates of Ni-pyrrhotite and Ni-pyrite.
Chemical analysis will reveal Ni³+ as a contaminant from the walls of the autoclave in which the synthetic aquamarine was grown.
Tairus first produced light to dark greenish blue synthetic aquamarine in Russia in the mid-1990s. It is synthesized hydrothermally, and owes its greenish color to small amounts of Fe²+ and a Fe²+ - Fe³+ charge transfer mechanism. It is grown as flat tabular crystals on seed plates oriented at an angle to the c-axis.
Hyrothermally grown synthetic aquamarine has the following gemological properties:
Color: Light to dark greenish blue
Specific gravity: 2.65 – 2.70
Refractive index: 1.587/1.580 – 1.571/1.577
Birefringence: 0.004/0.008
Pleochroism: Weak to strong blue/colorless
Fluorescence (UV): Inert
VIS absorption spectrum: Bands at 800nm (Fe²+ ), 375nm ( Fe³+ ), shoulder at 650nm (Fe²+ - Fe³+ charge transfer, line at 400nm (Ni³+)
It can be discriminated from natural aquamarine by its:
- Chevron-like growth banding that parallels the seed plate. This growth banding which is made up of pyramidal sub-cellular growth subunits is typical of hydrothermal growth occurring of seed plates oriented at an angle to its c-axis.
- Occasional presence of flake-like aggregates of Ni-pyrrhotite and Ni-pyrite.
Chemical analysis will reveal Ni³+ as a contaminant from the walls of the autoclave in which the synthetic aquamarine was grown.
Friday, March 30, 2007
Deep Diffusion Treatment Of Corundum
(via ICA Early Warning Flash, No. 32, February 16, 1990) GIA writes:
General background
At one of the gem shows held in Tucson, Arizona, during February of 1990 one exhibitor was offering for sale blue sapphires which were reportedly enhanced with a ‘deep’ diffusion treatment. The authors of this report were shown two plastic bags of reportedly treated material, each containing an estimated several hundred carats of these treated stones. A number of these were purchased for investigation.
Gemological properties
Eleven treated stones were examined. Basic gemological properties—refractive index, birefringence, optic character, Chelsea filter reaction—were all consistent with those reported in the literature for natural blue sapphires.
The color of the stones was fairly uniform, being a medium dark slightly violetish blue. All were very transparent.
None of the stones exhibited any absorption features of the type association with iron-bearing blue sapphires. Three of the stones, however, exhibited a bright fluorescent line centered at 693nm. It is interesting in this regard that the vendor’s promotional flier states that ‘….all stones treated are genuine Ceylon sapphires…’
Key identifying features
Under longwave ultraviolet radiation all but two of the stones were inert; these same stones all fluoresced a weak to moderate, chalky yellowish green to short wave ultraviolet. The other two stones fluoresced a weak to moderate pinkish orange to longwave ultraviolet; the shortwave reaction was similar but weaker in intensity. None of the stones exhibited any phosphorescence.
Magnification and darkfield illumination revealed some features associated with corundum that has been subjected to high temperatures: diffused color banding, broken ‘dot-like’ acicular inclusions, melted included crystals resembling ‘snowballs’ with surrounding spatter halos, and superficial sintering in surface pits. It should be noted that these features were, in general, minor.
Examination using diffused transmitted light without immersion or magnification showed color concentrations along facet junctions and outlining of the girdle edge. Also noted was some variation in color from one facet to another.
Using immersion and diffused transmitted light without magnification the color concentrations along facet junctions and the girdle as well as the uneven facet-to-facet coloration were again noted. In many cases these features were significantly more obvious when immersion was now used.
Suggestion
Diffusion treated sapphires are now being made increasingly available in the market. It this becomes important to use diffused transmitted illumination and immersion in the routine examination of corundum.
General background
At one of the gem shows held in Tucson, Arizona, during February of 1990 one exhibitor was offering for sale blue sapphires which were reportedly enhanced with a ‘deep’ diffusion treatment. The authors of this report were shown two plastic bags of reportedly treated material, each containing an estimated several hundred carats of these treated stones. A number of these were purchased for investigation.
Gemological properties
Eleven treated stones were examined. Basic gemological properties—refractive index, birefringence, optic character, Chelsea filter reaction—were all consistent with those reported in the literature for natural blue sapphires.
The color of the stones was fairly uniform, being a medium dark slightly violetish blue. All were very transparent.
None of the stones exhibited any absorption features of the type association with iron-bearing blue sapphires. Three of the stones, however, exhibited a bright fluorescent line centered at 693nm. It is interesting in this regard that the vendor’s promotional flier states that ‘….all stones treated are genuine Ceylon sapphires…’
Key identifying features
Under longwave ultraviolet radiation all but two of the stones were inert; these same stones all fluoresced a weak to moderate, chalky yellowish green to short wave ultraviolet. The other two stones fluoresced a weak to moderate pinkish orange to longwave ultraviolet; the shortwave reaction was similar but weaker in intensity. None of the stones exhibited any phosphorescence.
Magnification and darkfield illumination revealed some features associated with corundum that has been subjected to high temperatures: diffused color banding, broken ‘dot-like’ acicular inclusions, melted included crystals resembling ‘snowballs’ with surrounding spatter halos, and superficial sintering in surface pits. It should be noted that these features were, in general, minor.
Examination using diffused transmitted light without immersion or magnification showed color concentrations along facet junctions and outlining of the girdle edge. Also noted was some variation in color from one facet to another.
Using immersion and diffused transmitted light without magnification the color concentrations along facet junctions and the girdle as well as the uneven facet-to-facet coloration were again noted. In many cases these features were significantly more obvious when immersion was now used.
Suggestion
Diffusion treated sapphires are now being made increasingly available in the market. It this becomes important to use diffused transmitted illumination and immersion in the routine examination of corundum.
The Shawshank Redemption
Memorable quote (s) from the movie:
Andy Dufresne (Tim Robbins): You know what the Mexicans say about the Pacific?
Red (Morgan Freeman): No.
Andy Dufresne (Tim Robbins): They say it has no memory. That's where I want to live the rest of my life. A warm place with no memory.
Andy Dufresne (Tim Robbins): You know what the Mexicans say about the Pacific?
Red (Morgan Freeman): No.
Andy Dufresne (Tim Robbins): They say it has no memory. That's where I want to live the rest of my life. A warm place with no memory.
Hardness Testing Of Gemstones: A Re-evaluation Of The Values
(via Gemmology Queensland, Vol 3, No.1, Jan 2002/IGC Conference Madrid 2001) Michael Gray writes:
Hardness testing is one of the methods that a mineralogist uses to determine the identity of a mineral sample, but which has rarely been used by the gemologist. A mineralogist can usually find some inconspicuous face or broken area to conduct a scratch test, but the gemologist rarely has had a surface on a gemstone to do a comparable test without visible damage to the polish of the stone. However, the ability to choose a random surface may give a false value when a range of hardness exist, as in the case of kyanite, which has a documented variation from 4.5 to 5 on the Moh’s scale of hardness. While a species with such a diverse range can be easy to identify and test, there are many other species that have smaller variations that have not been measured. We are preparing a method of testing hardness during the faceting process. Our present system was developed by Friedrich Mohs in 1822, whereby he set relative values of hardness to ten easily obtainable species for comparison to each other, and measured by making scratches on surfaces of the unknown material with these ten species. This scale is still used as the standard, but variations in hardness has been known since at least 1844 using a device called sclerometer, and researchers were able to deduce objective values, although some variations in these scales are noted, depending upon the method and preparation used. In fact, some researchers determined that topaz is less hard than quartz when the sclerometer was used on powders of these two species.
Lapidaries have always noticed some of these variations in hardness in some species, especially noticeable in heat treated sapphires and rubies. A good example of this variation is the species fresnoite. In the references, the published hardness varies from “3 to 4” to a value of 4.7. A lapidary must rely upon these figures to determine which cutting and polishing laps and media to use in fashioning a gemstone. A great variation in hardness was noticed in the grinding and polishing of the stone, with only one direction being noticeably ‘soft’ as compared to the other facets. There is only one direction being in the range of 4 in hardness, with all other directions being noticeably harder.
These are hardly the only examples to cite; there are many materials, such as spodumene, sillimanite, elbaite, and many of the garnets that exhibit some noticeable variation in hardness during faceting. Diamond cutters know of the variations in their specialty, and use that knowledge in the fashioning of those gems.
The argument could be made that Moh’s scale has worked for almost two centuries, and that there is n need to change this system. That is not the purpose of this study. There are a number of purposes why this study has been initiated to determine the actual hardness of a species, such as fresnoite, where the original description may be inaccurate to document the variation of hardness, as well ad ‘normal’ hardness, within a species. To determine if a variation of hardness may be caused by a man-induced treatment, such as heat treatment of corundum, which then can be used as a way of detecting these treatments. This might also be taken further to determine origin, as well, depending upon impurities, coloring agents, and variations in chemical composition to help clear up conflicting values in different publications to relate these values to the existing Moh’s scale of hardness so that the numbers are understandable to academics and lay persons alike.
Equipment has been developed recently that makes it much easier to conduct hardness testing. The development of ultrasonic indenters that can be calibrated based on the Rockwell and Vickers scales, two of the glass and metal industry’s standards, should eliminate most of the danger of stone breakage during hardness testing. Our testing will be done during the cutting stages, so any noticeable marks made on the softer stones can be polished out.
The ten species used in the Moh’s scale will have been measured, resulting in a set of numbers that will set the parameters for the decimal places between species. Stones are being faceted of these materials to make note of any noticeable variations during cutting, and then measurements taken of these materials. After these values are established, checked, and documented, other species will be faceted, with noticeable hard and soft areas marked for testing. On stones with variable hardnesses, at least four hardness tests will be performed, one each on the ‘softest’ and ‘hardest’ directions, since these normally occur only in one direction, and several tests to establish the ‘normal’ hardness, the hardness over the rest of the material. Therefore, while a range may be established, a third number may represent the general hardness of the material.
The practicality of using gemstones for hardness testing is the general ‘purity’ of the sample being used. Many of the published hardness values were obtained using tiny pieces of the type specimens when they were first discovered and therefore were probably unable to get much accuracy, especially minerals described prior to the 1960s. Unfortunately, once a mineral is named and documented, the values may come up dependent upon the locality and/or if the material has been treated, and all of this information will be documented, as well, whenever possible. Ultimately, we should be able to document the crystal orientation that these variable hardnesses will occur.
There is also an important side benefit to this testing. While hardness testing is only used in a miniscule number of gem identifications, we hope to show that this test can be used in gem labs, using the modern equipment available today. The marks made by a skilled and knowledgeable worker using this modern equipment can be so tiny as to be undetectable by the naked eye, and can be placed on an inconspicuous spot on the girdle or pavilion of the stone. With the values obtained through this research, there will be one more test available for questionable gems. It should also be possible to test mounted stones as well, where refractive indices and specific gravities may not be able to be obtained without removal of the stone from the mounting.
Hardness testing is one of the methods that a mineralogist uses to determine the identity of a mineral sample, but which has rarely been used by the gemologist. A mineralogist can usually find some inconspicuous face or broken area to conduct a scratch test, but the gemologist rarely has had a surface on a gemstone to do a comparable test without visible damage to the polish of the stone. However, the ability to choose a random surface may give a false value when a range of hardness exist, as in the case of kyanite, which has a documented variation from 4.5 to 5 on the Moh’s scale of hardness. While a species with such a diverse range can be easy to identify and test, there are many other species that have smaller variations that have not been measured. We are preparing a method of testing hardness during the faceting process. Our present system was developed by Friedrich Mohs in 1822, whereby he set relative values of hardness to ten easily obtainable species for comparison to each other, and measured by making scratches on surfaces of the unknown material with these ten species. This scale is still used as the standard, but variations in hardness has been known since at least 1844 using a device called sclerometer, and researchers were able to deduce objective values, although some variations in these scales are noted, depending upon the method and preparation used. In fact, some researchers determined that topaz is less hard than quartz when the sclerometer was used on powders of these two species.
Lapidaries have always noticed some of these variations in hardness in some species, especially noticeable in heat treated sapphires and rubies. A good example of this variation is the species fresnoite. In the references, the published hardness varies from “3 to 4” to a value of 4.7. A lapidary must rely upon these figures to determine which cutting and polishing laps and media to use in fashioning a gemstone. A great variation in hardness was noticed in the grinding and polishing of the stone, with only one direction being noticeably ‘soft’ as compared to the other facets. There is only one direction being in the range of 4 in hardness, with all other directions being noticeably harder.
These are hardly the only examples to cite; there are many materials, such as spodumene, sillimanite, elbaite, and many of the garnets that exhibit some noticeable variation in hardness during faceting. Diamond cutters know of the variations in their specialty, and use that knowledge in the fashioning of those gems.
The argument could be made that Moh’s scale has worked for almost two centuries, and that there is n need to change this system. That is not the purpose of this study. There are a number of purposes why this study has been initiated to determine the actual hardness of a species, such as fresnoite, where the original description may be inaccurate to document the variation of hardness, as well ad ‘normal’ hardness, within a species. To determine if a variation of hardness may be caused by a man-induced treatment, such as heat treatment of corundum, which then can be used as a way of detecting these treatments. This might also be taken further to determine origin, as well, depending upon impurities, coloring agents, and variations in chemical composition to help clear up conflicting values in different publications to relate these values to the existing Moh’s scale of hardness so that the numbers are understandable to academics and lay persons alike.
Equipment has been developed recently that makes it much easier to conduct hardness testing. The development of ultrasonic indenters that can be calibrated based on the Rockwell and Vickers scales, two of the glass and metal industry’s standards, should eliminate most of the danger of stone breakage during hardness testing. Our testing will be done during the cutting stages, so any noticeable marks made on the softer stones can be polished out.
The ten species used in the Moh’s scale will have been measured, resulting in a set of numbers that will set the parameters for the decimal places between species. Stones are being faceted of these materials to make note of any noticeable variations during cutting, and then measurements taken of these materials. After these values are established, checked, and documented, other species will be faceted, with noticeable hard and soft areas marked for testing. On stones with variable hardnesses, at least four hardness tests will be performed, one each on the ‘softest’ and ‘hardest’ directions, since these normally occur only in one direction, and several tests to establish the ‘normal’ hardness, the hardness over the rest of the material. Therefore, while a range may be established, a third number may represent the general hardness of the material.
The practicality of using gemstones for hardness testing is the general ‘purity’ of the sample being used. Many of the published hardness values were obtained using tiny pieces of the type specimens when they were first discovered and therefore were probably unable to get much accuracy, especially minerals described prior to the 1960s. Unfortunately, once a mineral is named and documented, the values may come up dependent upon the locality and/or if the material has been treated, and all of this information will be documented, as well, whenever possible. Ultimately, we should be able to document the crystal orientation that these variable hardnesses will occur.
There is also an important side benefit to this testing. While hardness testing is only used in a miniscule number of gem identifications, we hope to show that this test can be used in gem labs, using the modern equipment available today. The marks made by a skilled and knowledgeable worker using this modern equipment can be so tiny as to be undetectable by the naked eye, and can be placed on an inconspicuous spot on the girdle or pavilion of the stone. With the values obtained through this research, there will be one more test available for questionable gems. It should also be possible to test mounted stones as well, where refractive indices and specific gravities may not be able to be obtained without removal of the stone from the mounting.
Elements Of Physical Geology
By James H Zumberge & Clemens A Nelson
John Wiley & Sons, Inc
1976 ISBN 0-471-98674-7
James H Zumberge & Clemens A Nelson writes:
This book is a direct outgrowth of our Elements of Geology, Third Edition. It is intended for a one-term course in physical geology for the nonmajor. Because we think that a historical perspective is essential to the understanding of earth science, a number of items commonly reserved for books on earth history are included in Chapter 6, Geologic Time. To provide for an appreciation of geologic time in the earlier chapters, the geologic time scale is introduced in the first chapter.
Although many recent text have used the exciting developments in sea floor spreading and place tectonics as a theme around which to organize the subject matter of physical geology, we have preferred the more traditional approach for pedagogic reasons. We believe that an investigation of the earth from the inside out provides a better basis on which student can begin to understand his environment. Thus, the first nine chapters deal with the fundamental materials of the earth and its internal characteristics and processes; the following seven chapters deal with processes that have shaped the surface of the earth and provided its infinite variety of topographic forms.
It is also common practice for current texts to devote a single unit to Environmental Geology. We believe that geology has always been a fundamental environmental science and that the subject of the environment, including geologic hazards, is better served by its inclusion in the chapters where it is natural part of the subject under discussion. Thus, the reader will find environmental problems treated in the chapters on volcanoes, earthquakes, climate, landslides, groundwater, rivers, wind, glaciers, oceans, and resources.
The text of most chapters from Elements of Geology has been revised, and new illustrations have been added. The materials can structures of the crust of the earth are treated in chapter 3, Materials of the Earth’s Crust, and chapter 4, Structures of the Earth’s Crust. These subjects were incorporated into a single chapter in Elements of Geology. Chapter 9, Global Tectonics and Mountain Building, has been revised and expanded and includes a historical account of mountain building theories and a detailed account of the new revolution in geology—that of sea floor spreading and plate tectonics. In each of the chapters dealing with surface processes (chapters 10 to 16), examples from the geologic record have been included to illustrate the uniformitarian relationships between present observations and the past record of the earth.
Chapter 17, Resources from the Earth, is new; it incorporates a number of separate discussions from Elements of Geology and current problems of environmental geology and mineral and energy resources.
We are grateful to the people who supplied photographs for this book. We particularly thank Tad Nichols of Tucson, Arizona, for providing many outstanding photographs of geologic features and phenomena. Sources are given for all photographic illustrations except the ones taken by us. We also thank the National Geographic Society for permission to use parts of their colored maps of the Atlantic and Pacific Ocean floors, which appear as Plates V and VI, preceding Chapter 9. Again we thank Derwin Bell of the Department of Geology at the University of Michigan whose excellent illustrations from Elements of Geology have served so well. We also thank Jeanie Martinez of the Department of Geology, University of California, Los Angeles, for several additional illustrations, and Kathyryn Brown at the University of California, Los Angeles, for help in manuscript preparation.
A great many people have made general and specific contributions in the preparation of the book. Our colleagues in the College of Earth Sciences at the University of Arizona, the Department of Geology, University of Nebraska, and the Department of Geology, University of California, Los Angeles, have been especially generous of their expertise. Don Deneck of Wiley has been both a spur and helpful associate during the many stages of preparation. We express our gratitude to our wives, Marilyn Zumberge and Ruth Nelson, for their patience and understanding while this book was being written.
John Wiley & Sons, Inc
1976 ISBN 0-471-98674-7
James H Zumberge & Clemens A Nelson writes:
This book is a direct outgrowth of our Elements of Geology, Third Edition. It is intended for a one-term course in physical geology for the nonmajor. Because we think that a historical perspective is essential to the understanding of earth science, a number of items commonly reserved for books on earth history are included in Chapter 6, Geologic Time. To provide for an appreciation of geologic time in the earlier chapters, the geologic time scale is introduced in the first chapter.
Although many recent text have used the exciting developments in sea floor spreading and place tectonics as a theme around which to organize the subject matter of physical geology, we have preferred the more traditional approach for pedagogic reasons. We believe that an investigation of the earth from the inside out provides a better basis on which student can begin to understand his environment. Thus, the first nine chapters deal with the fundamental materials of the earth and its internal characteristics and processes; the following seven chapters deal with processes that have shaped the surface of the earth and provided its infinite variety of topographic forms.
It is also common practice for current texts to devote a single unit to Environmental Geology. We believe that geology has always been a fundamental environmental science and that the subject of the environment, including geologic hazards, is better served by its inclusion in the chapters where it is natural part of the subject under discussion. Thus, the reader will find environmental problems treated in the chapters on volcanoes, earthquakes, climate, landslides, groundwater, rivers, wind, glaciers, oceans, and resources.
The text of most chapters from Elements of Geology has been revised, and new illustrations have been added. The materials can structures of the crust of the earth are treated in chapter 3, Materials of the Earth’s Crust, and chapter 4, Structures of the Earth’s Crust. These subjects were incorporated into a single chapter in Elements of Geology. Chapter 9, Global Tectonics and Mountain Building, has been revised and expanded and includes a historical account of mountain building theories and a detailed account of the new revolution in geology—that of sea floor spreading and plate tectonics. In each of the chapters dealing with surface processes (chapters 10 to 16), examples from the geologic record have been included to illustrate the uniformitarian relationships between present observations and the past record of the earth.
Chapter 17, Resources from the Earth, is new; it incorporates a number of separate discussions from Elements of Geology and current problems of environmental geology and mineral and energy resources.
We are grateful to the people who supplied photographs for this book. We particularly thank Tad Nichols of Tucson, Arizona, for providing many outstanding photographs of geologic features and phenomena. Sources are given for all photographic illustrations except the ones taken by us. We also thank the National Geographic Society for permission to use parts of their colored maps of the Atlantic and Pacific Ocean floors, which appear as Plates V and VI, preceding Chapter 9. Again we thank Derwin Bell of the Department of Geology at the University of Michigan whose excellent illustrations from Elements of Geology have served so well. We also thank Jeanie Martinez of the Department of Geology, University of California, Los Angeles, for several additional illustrations, and Kathyryn Brown at the University of California, Los Angeles, for help in manuscript preparation.
A great many people have made general and specific contributions in the preparation of the book. Our colleagues in the College of Earth Sciences at the University of Arizona, the Department of Geology, University of Nebraska, and the Department of Geology, University of California, Los Angeles, have been especially generous of their expertise. Don Deneck of Wiley has been both a spur and helpful associate during the many stages of preparation. We express our gratitude to our wives, Marilyn Zumberge and Ruth Nelson, for their patience and understanding while this book was being written.
The Founders Of Geology
By Sir Andrew Geikie
Dover Publications, Inc
1962
Dover Publication writes:
The later half of the 19th century and the first two decades of the 20th century are especially interesting to students of geology, for it was during those seventy years that the main modern foundations of the science were laid. This book surveys the high moments and central figures in that era of seminal geological activity.
It recounts the story of the progress of geological ideas by reviewing the careers of some of the leaders by whom the progress was chiefly effected, giving full consideration to the lives and work of these major figures, and indicating in the process how geological ideas arose and were slowly worked out into the forms which they now wear. Some of the men whose careers and contributions are examined are Palissy, Guettard, Desmarest, Pallas, De Saussure, Arduino, Lehman, Fuchsel, Werner, Hutton, Playfair, Sir James Hall, Giraud-Soulavie, Cuvier, Michell, Lyell, Logan, Darwin, Agassiz, Nicol, and others.
The author discusses such matters as geological ideas among the Greeks and Romans; growth of geological ideas in the Middle Ages; scientific cosmogonists—Descartes and Leibnitz; the rise of geology in France; the foundation of volcanic geology; the rise of geological travel; the history of the doctrine of geological succession; the Wernerian school of geology; the rise of the modern conception of the theory of the earth; the birth of experimental geology; the rise of stratigraphical geology and paleontology; early teachers and textbooks; the transition or Greywacke formation resolved into the Cambrian, Silurian and Devonian systems; the primordial fauna of Barrande; the pre-Cambrian rocks first begun to be set in order; the influence of Darwin; adoption of zonal stratigraphy of fossiliferous rocks; the rise of glacial geology; the development of geological map-making in Europe and North America; the rise of petrographical geology; and other related topics.
Dover Publications, Inc
1962
Dover Publication writes:
The later half of the 19th century and the first two decades of the 20th century are especially interesting to students of geology, for it was during those seventy years that the main modern foundations of the science were laid. This book surveys the high moments and central figures in that era of seminal geological activity.
It recounts the story of the progress of geological ideas by reviewing the careers of some of the leaders by whom the progress was chiefly effected, giving full consideration to the lives and work of these major figures, and indicating in the process how geological ideas arose and were slowly worked out into the forms which they now wear. Some of the men whose careers and contributions are examined are Palissy, Guettard, Desmarest, Pallas, De Saussure, Arduino, Lehman, Fuchsel, Werner, Hutton, Playfair, Sir James Hall, Giraud-Soulavie, Cuvier, Michell, Lyell, Logan, Darwin, Agassiz, Nicol, and others.
The author discusses such matters as geological ideas among the Greeks and Romans; growth of geological ideas in the Middle Ages; scientific cosmogonists—Descartes and Leibnitz; the rise of geology in France; the foundation of volcanic geology; the rise of geological travel; the history of the doctrine of geological succession; the Wernerian school of geology; the rise of the modern conception of the theory of the earth; the birth of experimental geology; the rise of stratigraphical geology and paleontology; early teachers and textbooks; the transition or Greywacke formation resolved into the Cambrian, Silurian and Devonian systems; the primordial fauna of Barrande; the pre-Cambrian rocks first begun to be set in order; the influence of Darwin; adoption of zonal stratigraphy of fossiliferous rocks; the rise of glacial geology; the development of geological map-making in Europe and North America; the rise of petrographical geology; and other related topics.
Thursday, March 29, 2007
Manufacturing, Production, And Trade Of Synthetic And Enhanced Gems In Modern Russia
(via Gemmology Queensland, Vol 3, No.1, Jan 2002/IGC Conference Madrid 2001) Vladimir S Balitsky writes:
Synthetic gems
In modern Russia in industrial scales practically all kinds and varieties of synthetic analogues of natural gems are produced as well as it was in former USSR. Moreover, crystals of the whole row of compounds having no analogues in nature but possessing properties of gems are synthesized. A list of all synthetic gems produced at present in Russia is given in Table 1 with methods of their obtaining approximate volumes of production and their prices. As can be seen, leuco-sapphire, ruby and sapphires are produced in large quantities. They are grown mainly from the melt by the methods of Verneuil, Czochralski, Kyropulus and Zone melting. Lately they have been grown in small quantities by hydrothermal and flux methods. Traditional Russian synthetic gems also include quartz and its colored varieties especially amethyst, citrine, blue and green quartz. Lately they have developed new technologies of producing two colored amethyst-citrine quartz (ametrine), pink transparent phosphorous-bearing quartz and unusual copper-bearing aventurine in small quantities. Under artificial conditions drusses of both colorless and colored quartz are also grown.
Table 1
Synthetic gems produced in Russia at present
Name: Alexandrite
Growth technique: Czochralski
Approximate production/kg per year: up to one hundred
Approximate price of raw material (US$/per kg): 1000 – 7500
Name: Alexandrite
Growth technique: Flux
Approximate production/kg per year: a few kg’s
Approximate price of raw material (US$/per kg): 1000 – 7500
Name: Amethyst
Growth technique: Hydrothermal
Approximate production/kg per year: a few thousand
Approximate price of raw material (US$/per kg): 50 – 150
Name: Ametrine
Growth technique: Hydrothermal
Approximate production/kg per year: a few hundred
Approximate price of raw material (US$/per kg): 100 - 150
Name: Aquamarine
Growth technique: Hydrothermal/Flux
Approximate production/kg per year: a few
Approximate price of raw material (US$/per kg): 3000 – 5000
Name: Cubic Zirconium Oxide (CZ)
Growth technique: Skull Melting
Approximate production/kg per year: a few thousand
Approximate price of raw material (US$/per kg): 30 – 60
Name: Diamond
Growth technique: HPHT
Approximate production/kg per year: up to 2
Approximate price of raw material (US$/per kg): 1000000
Name: Emerald
Growth technique: Hydrothermal / Flux
Approximate production/kg per year: up to 50
Approximate price of raw material (US$/per kg): 5000 – 7500
Name: Emerald Drusses
Growth technique: Flux
Approximate production/kg per year: a few
Approximate price of raw material (US$/per kg): 1000 – 15000
Name: Forsterite
Growth technique: Czochralski
Approximate production/kg per year: a few
Approximate price of raw material (US$/per kg): 5000
Name: Gadolium Gallium Garnet (GGG)
Growth technique: Czochralski
Approximate production/kg per year: a few dozen
Approximate price of raw material (US$/per kg): 10000
Name: Leuco sapphire
Growth technique: Czochralski
Approximate production/kg per year: a few thousand
Approximate price of raw material (US$/per kg): 350 - 400
Name: Leuco sapphire
Growth technique: Vernueil
Approximate production/kg per year: a few thousand
Approximate price of raw material (US$/per kg): 250 – 300
Name: Leuco sapphire
Growth technique: Kyropulus
Approximate production/kg per year: a few thousand
Approximate price of raw material (US$/per kg): 350 - 400
Name: Leuco sapphire
Growth technique: Horizontal Zoning Melt
Approximate production/kg per year: a few thousand
Approximate price of raw material (US$/per kg): 400 – 500
Name: Morganite
Growth technique: Hydrothermal / Flux
Approximate production/kg per year: a few
Approximate price of raw material (US$/per kg): 3000 – 7000
Name: Malachite
Growth technique: Chemical precipitation from aqueous solutions
Approximate production/kg per year: up to thousand
Approximate price of raw material (US$/per kg): 40 -70
Name: Moissanite
Growth technique: High pressure sublimation
Approximate production/kg per year: a few dozen
Approximate price of raw material (US$/per kg): 25000 – 50000
Name: Opal noble
Growth technique: Chemical precipitation + impregnation by plastic or zirconium hydroxide or silica + high temperature treatment
Approximate production/kg per year: a few dozen
Approximate price of raw material (US$/per kg): 20000 – 35000
Name: Quartz colorless
Growth technique: Hydrothermal
Approximate production/kg per year: a few hundreds of thousands
Approximate price of raw material (US$/per kg): 40 – 600
Name: Quartz colored (yellow, green, blue, brown, smoky, milky)
Growth technique: Hydrothermal
Approximate production/kg per year: a few hundreds of thousands
Approximate price of raw material (US$/per kg): 40 – 80
Name: Quartz pink (transparent)
Growth technique: Hydrothermal
Approximate production/kg per year: a few dozens
Approximate price of raw material (US$/per kg): 3000 - 5000
Name: Quartz drusses
Growth technique: Hydrothermal
Approximate production/kg per year: a few dozens
Approximate price of raw material (US$/per kg): 50 – 100
Name: Ruby
Growth technique: Vernueil / Czochralski / Horizontal Zoning Melt
Approximate production/kg per year: a few thousands
Approximate price of raw material (US$/per kg): 250 – 1000
Name: Ruby
Growth technique: Hydrothermal
Approximate production/kg per year: a few
Approximate price of raw material (US$/per kg): 5000 - 10000
Name: Sapphire
Growth technique: Verneuil / Czochralski
Approximate production/kg per year: a few thousands
Approximate price of raw material (US$/per kg): 250 – 1000
Name: Sapphire
Growth technique: Hydrothermal
Approximate production/kg per year: a few
Approximate price of raw material (US$/per kg): 5000 – 10000
Name: Spinel
Growth technique: Flux
Approximate production/kg per year: a few
Approximate price of raw material (US$/per kg): 25000
Name: Spinel drusses
Growth technique: Flux
Approximate production/kg per year: a few
Approximate price of raw material (US$/per kg): 25000
Name: Turquoise
Growth technique: Chemical precipitation + high pressure treatment
Approximate production/kg per year: a few hundreds
Approximate price of raw material (US$/per kg): 50 – 80
Name: Yttrium Aluminum Garnet (YAG) (Colorless and colored)
Growth technique: Czochralski / Horizontal Zone Melting
Approximate production/kg per year: a few thousands
Approximate price of raw material (US$/per kg): 400 – 700
Name: Zincate
Growth technique: Hydrothermal
Approximate production/kg per year: a few
Approximate price of raw material (US$/per kg): 30000
An essential role in the production of synthetic gems in modern Russia belongs to emerald. It is mainly grown under hydrothermal conditions, but in small quantities it is obtained from flux. Besides emerald, other colored varieties of beryl are grown in very limited quantities. Among other popular synthetic gems grown in Russia, one should notice alexandrite and spinel. First, it was grown by Czochralski and flux methods, and then by Verneuil and flux. The most precious of them are crystals grown from flux. Among other synthetic gems, refined black and white noble opal is also produced. The material may look very similar to the natural opal. Synthetic malachite has also been produced successfully. A considerable progress has been made in the synthesis of large diamonds (yellow, blue and colorless) with the maximum weight up to 5 ct. Within the last two years synthetic moissanite has also been produced. However both synthetic diamonds and synthetic moissanites are produced in rather restricted quantities.
Enhanced gems
Many gems found and imported into Russia (corundum, topaz, quartz, garnet, danburite, scapolite, beryl, tourmaline, turquoise, coral, charoite, lazurite, agates etc.) are of low quality. The gems are often subjected to enhancement with the purpose of increasing their quality. Table 2 gives a list of stones with indicative treatments.
Name: Agate (chalcedony)
Enhancement process: impregnation / heat treatment / irradiation
Enhancement effect: pale colors to yellow, brown, green, blue, black and red; pale colors to brown and red; change of color to dark gray.
Name: Amazonite
Enhancement process: heat treatment / dyeing
Enhancement effect: improvement of color
Name: Amber
Enhancement process: reconstruction / heat treatment / pressing
Enhancement effect: augmentation of weight; improvement of inner structure with induced cracking; augmentation of weight
Name: Charoite
Enhancement process: dyeing
Enhancement effect: improvement of color
Name: Corundum (colorless and colored)
Enhancement process: heat treatment / heat treatment with diffusion / surface coating
Enhancement effect: colorless and pale colors to blue
Name: Danburite
Enhancement process: irradiation / heat treatment
Enhancement effect: remove colorless to brownish—pink / fading
Name: Heliodor
Enhancement process: heat treatment
Enhancement effect: remove yellow to blue (aquamarine)
Name: Lazurite
Enhancement process: impregnation / heat treatment
Enhancement effect: improvement of color
Name: Nephrite
Enhancement process: hydrothermal treatment / irradiation
Enhancement effect: lightening of dark green color to white / darkening of green and brown to black
Name: Quartz
Enhancement process: heat treatment / irradiation / surface coating
Enhancement effect: dark smoky to pale smoky or greenish yellow or colorless / colorless and pale colors to smoky or greenish yellow / colorless and pale colors to pink or blue
Name: Radonite
Enhancement process: dyeing
Enhancement effect: improvement of color
Name: Topaz
Enhancement process: irradiation / irradiation + heat treatment
Enhancement effect: colorless and pale colors to yellow brown or reddish brown / colorless or brown to brownish green or blue / brown or orange to pink / brown or green or blue to colorless
Name: Turquoise
Enhancement process: impregnation under high temperature and high pressure
Enhancement effect: improvement of color / rise of hardness
Synthetic gems
In modern Russia in industrial scales practically all kinds and varieties of synthetic analogues of natural gems are produced as well as it was in former USSR. Moreover, crystals of the whole row of compounds having no analogues in nature but possessing properties of gems are synthesized. A list of all synthetic gems produced at present in Russia is given in Table 1 with methods of their obtaining approximate volumes of production and their prices. As can be seen, leuco-sapphire, ruby and sapphires are produced in large quantities. They are grown mainly from the melt by the methods of Verneuil, Czochralski, Kyropulus and Zone melting. Lately they have been grown in small quantities by hydrothermal and flux methods. Traditional Russian synthetic gems also include quartz and its colored varieties especially amethyst, citrine, blue and green quartz. Lately they have developed new technologies of producing two colored amethyst-citrine quartz (ametrine), pink transparent phosphorous-bearing quartz and unusual copper-bearing aventurine in small quantities. Under artificial conditions drusses of both colorless and colored quartz are also grown.
Table 1
Synthetic gems produced in Russia at present
Name: Alexandrite
Growth technique: Czochralski
Approximate production/kg per year: up to one hundred
Approximate price of raw material (US$/per kg): 1000 – 7500
Name: Alexandrite
Growth technique: Flux
Approximate production/kg per year: a few kg’s
Approximate price of raw material (US$/per kg): 1000 – 7500
Name: Amethyst
Growth technique: Hydrothermal
Approximate production/kg per year: a few thousand
Approximate price of raw material (US$/per kg): 50 – 150
Name: Ametrine
Growth technique: Hydrothermal
Approximate production/kg per year: a few hundred
Approximate price of raw material (US$/per kg): 100 - 150
Name: Aquamarine
Growth technique: Hydrothermal/Flux
Approximate production/kg per year: a few
Approximate price of raw material (US$/per kg): 3000 – 5000
Name: Cubic Zirconium Oxide (CZ)
Growth technique: Skull Melting
Approximate production/kg per year: a few thousand
Approximate price of raw material (US$/per kg): 30 – 60
Name: Diamond
Growth technique: HPHT
Approximate production/kg per year: up to 2
Approximate price of raw material (US$/per kg): 1000000
Name: Emerald
Growth technique: Hydrothermal / Flux
Approximate production/kg per year: up to 50
Approximate price of raw material (US$/per kg): 5000 – 7500
Name: Emerald Drusses
Growth technique: Flux
Approximate production/kg per year: a few
Approximate price of raw material (US$/per kg): 1000 – 15000
Name: Forsterite
Growth technique: Czochralski
Approximate production/kg per year: a few
Approximate price of raw material (US$/per kg): 5000
Name: Gadolium Gallium Garnet (GGG)
Growth technique: Czochralski
Approximate production/kg per year: a few dozen
Approximate price of raw material (US$/per kg): 10000
Name: Leuco sapphire
Growth technique: Czochralski
Approximate production/kg per year: a few thousand
Approximate price of raw material (US$/per kg): 350 - 400
Name: Leuco sapphire
Growth technique: Vernueil
Approximate production/kg per year: a few thousand
Approximate price of raw material (US$/per kg): 250 – 300
Name: Leuco sapphire
Growth technique: Kyropulus
Approximate production/kg per year: a few thousand
Approximate price of raw material (US$/per kg): 350 - 400
Name: Leuco sapphire
Growth technique: Horizontal Zoning Melt
Approximate production/kg per year: a few thousand
Approximate price of raw material (US$/per kg): 400 – 500
Name: Morganite
Growth technique: Hydrothermal / Flux
Approximate production/kg per year: a few
Approximate price of raw material (US$/per kg): 3000 – 7000
Name: Malachite
Growth technique: Chemical precipitation from aqueous solutions
Approximate production/kg per year: up to thousand
Approximate price of raw material (US$/per kg): 40 -70
Name: Moissanite
Growth technique: High pressure sublimation
Approximate production/kg per year: a few dozen
Approximate price of raw material (US$/per kg): 25000 – 50000
Name: Opal noble
Growth technique: Chemical precipitation + impregnation by plastic or zirconium hydroxide or silica + high temperature treatment
Approximate production/kg per year: a few dozen
Approximate price of raw material (US$/per kg): 20000 – 35000
Name: Quartz colorless
Growth technique: Hydrothermal
Approximate production/kg per year: a few hundreds of thousands
Approximate price of raw material (US$/per kg): 40 – 600
Name: Quartz colored (yellow, green, blue, brown, smoky, milky)
Growth technique: Hydrothermal
Approximate production/kg per year: a few hundreds of thousands
Approximate price of raw material (US$/per kg): 40 – 80
Name: Quartz pink (transparent)
Growth technique: Hydrothermal
Approximate production/kg per year: a few dozens
Approximate price of raw material (US$/per kg): 3000 - 5000
Name: Quartz drusses
Growth technique: Hydrothermal
Approximate production/kg per year: a few dozens
Approximate price of raw material (US$/per kg): 50 – 100
Name: Ruby
Growth technique: Vernueil / Czochralski / Horizontal Zoning Melt
Approximate production/kg per year: a few thousands
Approximate price of raw material (US$/per kg): 250 – 1000
Name: Ruby
Growth technique: Hydrothermal
Approximate production/kg per year: a few
Approximate price of raw material (US$/per kg): 5000 - 10000
Name: Sapphire
Growth technique: Verneuil / Czochralski
Approximate production/kg per year: a few thousands
Approximate price of raw material (US$/per kg): 250 – 1000
Name: Sapphire
Growth technique: Hydrothermal
Approximate production/kg per year: a few
Approximate price of raw material (US$/per kg): 5000 – 10000
Name: Spinel
Growth technique: Flux
Approximate production/kg per year: a few
Approximate price of raw material (US$/per kg): 25000
Name: Spinel drusses
Growth technique: Flux
Approximate production/kg per year: a few
Approximate price of raw material (US$/per kg): 25000
Name: Turquoise
Growth technique: Chemical precipitation + high pressure treatment
Approximate production/kg per year: a few hundreds
Approximate price of raw material (US$/per kg): 50 – 80
Name: Yttrium Aluminum Garnet (YAG) (Colorless and colored)
Growth technique: Czochralski / Horizontal Zone Melting
Approximate production/kg per year: a few thousands
Approximate price of raw material (US$/per kg): 400 – 700
Name: Zincate
Growth technique: Hydrothermal
Approximate production/kg per year: a few
Approximate price of raw material (US$/per kg): 30000
An essential role in the production of synthetic gems in modern Russia belongs to emerald. It is mainly grown under hydrothermal conditions, but in small quantities it is obtained from flux. Besides emerald, other colored varieties of beryl are grown in very limited quantities. Among other popular synthetic gems grown in Russia, one should notice alexandrite and spinel. First, it was grown by Czochralski and flux methods, and then by Verneuil and flux. The most precious of them are crystals grown from flux. Among other synthetic gems, refined black and white noble opal is also produced. The material may look very similar to the natural opal. Synthetic malachite has also been produced successfully. A considerable progress has been made in the synthesis of large diamonds (yellow, blue and colorless) with the maximum weight up to 5 ct. Within the last two years synthetic moissanite has also been produced. However both synthetic diamonds and synthetic moissanites are produced in rather restricted quantities.
Enhanced gems
Many gems found and imported into Russia (corundum, topaz, quartz, garnet, danburite, scapolite, beryl, tourmaline, turquoise, coral, charoite, lazurite, agates etc.) are of low quality. The gems are often subjected to enhancement with the purpose of increasing their quality. Table 2 gives a list of stones with indicative treatments.
Name: Agate (chalcedony)
Enhancement process: impregnation / heat treatment / irradiation
Enhancement effect: pale colors to yellow, brown, green, blue, black and red; pale colors to brown and red; change of color to dark gray.
Name: Amazonite
Enhancement process: heat treatment / dyeing
Enhancement effect: improvement of color
Name: Amber
Enhancement process: reconstruction / heat treatment / pressing
Enhancement effect: augmentation of weight; improvement of inner structure with induced cracking; augmentation of weight
Name: Charoite
Enhancement process: dyeing
Enhancement effect: improvement of color
Name: Corundum (colorless and colored)
Enhancement process: heat treatment / heat treatment with diffusion / surface coating
Enhancement effect: colorless and pale colors to blue
Name: Danburite
Enhancement process: irradiation / heat treatment
Enhancement effect: remove colorless to brownish—pink / fading
Name: Heliodor
Enhancement process: heat treatment
Enhancement effect: remove yellow to blue (aquamarine)
Name: Lazurite
Enhancement process: impregnation / heat treatment
Enhancement effect: improvement of color
Name: Nephrite
Enhancement process: hydrothermal treatment / irradiation
Enhancement effect: lightening of dark green color to white / darkening of green and brown to black
Name: Quartz
Enhancement process: heat treatment / irradiation / surface coating
Enhancement effect: dark smoky to pale smoky or greenish yellow or colorless / colorless and pale colors to smoky or greenish yellow / colorless and pale colors to pink or blue
Name: Radonite
Enhancement process: dyeing
Enhancement effect: improvement of color
Name: Topaz
Enhancement process: irradiation / irradiation + heat treatment
Enhancement effect: colorless and pale colors to yellow brown or reddish brown / colorless or brown to brownish green or blue / brown or orange to pink / brown or green or blue to colorless
Name: Turquoise
Enhancement process: impregnation under high temperature and high pressure
Enhancement effect: improvement of color / rise of hardness
Tootsie
Memorable quote (s) from the movie:
Michael Dorsey (Dustin Hoffman): Are you saying that nobody in New York will work with me?
George Fields (Sydney Pollack): No, no, that's too limited... nobody in Hollywood wants to work with you either. I can't even send you up for a commercial. You played a tomato for 30 seconds - they went a half a day over schedule because you wouldn't sit down.
Michael Dorsey (Dustin Hoffman): Yes - it wasn't logical.
George Fields (Sydney Pollack): You were a tomato. A tomato doesn't have logic. A tomato can't move.
Michael Dorsey (Dustin Hoffman): That's what I said. So if he can't move, how's he gonna sit down, George? I was a stand-up tomato: a juicy, sexy, beefsteak tomato. Nobody does vegetables like me. I did an evening of vegetables off-Broadway. I did the best tomato, the best cucumber... I did an endive salad that knocked the critics on their ass.
Michael Dorsey (Dustin Hoffman): Are you saying that nobody in New York will work with me?
George Fields (Sydney Pollack): No, no, that's too limited... nobody in Hollywood wants to work with you either. I can't even send you up for a commercial. You played a tomato for 30 seconds - they went a half a day over schedule because you wouldn't sit down.
Michael Dorsey (Dustin Hoffman): Yes - it wasn't logical.
George Fields (Sydney Pollack): You were a tomato. A tomato doesn't have logic. A tomato can't move.
Michael Dorsey (Dustin Hoffman): That's what I said. So if he can't move, how's he gonna sit down, George? I was a stand-up tomato: a juicy, sexy, beefsteak tomato. Nobody does vegetables like me. I did an evening of vegetables off-Broadway. I did the best tomato, the best cucumber... I did an endive salad that knocked the critics on their ass.
Subscribe to:
Posts (Atom)