Chemistry: Sodium potassium ferric silicate
Crystal system: Hexagonal; massive.
Color: Opaque; light to dark violet to reddish purple (Mg); color-change (blue purple: daylight; reddish purple: incandescent light).
Hardness: 6 – 6.5
Cleavage: Fracture: granular
Specific gravity: 2.74 mean; varies.
Refractive index: 1.607 – 1.610 (1.61 mean); Uniaxial negative.
Luster: Vitreous to waxy.
Dispersion:-
Dichroism: -
Occurrence: Vein infillings intergrown with other minerals; South Africa, Nambia.
Notes
Discovered in 1976; trade names include Royal Lavulite, Royal Azel; ornamental bead, cabochon, carvings; mineralogical name: manganaoan sugilite; constants may vary due to the presence of other manganese minerals; spectrum: broad absorption at 620 and 480nm, 4 sharp bands in blue and violet.
Friday, August 17, 2007
Thursday, August 16, 2007
Feeding Your Brain: New Benefits Found In Chocolate
Julie Steenhuysen writes about the effects on the brain of flavanols, an ingredient found in cocoa + other viewpoints @ http://www.reuters.com/article/scienceNews/idUSN1836014620070218
I think it's time that chocolates are prescribed for jewelers, gemologist, lab gemologists, diamond + colored stone dealers / graders, artists + consumers, before meal (s), at least three times a day, for better blood flow to the brain when they are at work + the experts believe that chocolates could also hold promise for treating some vascular impairments. It would be an educational experieince to test diamond/colored stone (s) grade (s) before/after chocolate medication, and see if the grade (s) are consistent. If there are overlaps, you be the judge. Just do it.
I think it's time that chocolates are prescribed for jewelers, gemologist, lab gemologists, diamond + colored stone dealers / graders, artists + consumers, before meal (s), at least three times a day, for better blood flow to the brain when they are at work + the experts believe that chocolates could also hold promise for treating some vascular impairments. It would be an educational experieince to test diamond/colored stone (s) grade (s) before/after chocolate medication, and see if the grade (s) are consistent. If there are overlaps, you be the judge. Just do it.
Can You Identify This Stone?
(via The Canadian Gemmologist, Vol.III, No.4, Spring, 1982) My color is caused by copper and I am considered idiochromatic. If you put acid on me, I fizz like a shaken bottle of cola. Monoclinic in structure, with an R.I somewhere between 1.65 – 1.90, I am used for jewelry and for carving. What am I?
Answer: Malachite
Answer: Malachite
The End Of Poverty
Good Books: (via Emergic) Jeffrey Sachs's book The End of Poverty: Economic Possibilities for Our Time is an almost-true revelation of today's state of the world. A good book for tomorrow's entrepreneurs.
The Amazon review provides an introduction:
Celebrated economist Jeffrey Sachs has a plan to eliminate extreme poverty around the world by 2025. If you think that is too ambitious or wildly unrealistic, you need to read this book. His focus is on the one billion poorest individuals around the world who are caught in a poverty trap of disease, physical isolation, environmental stress, political instability, and lack of access to capital, technology, medicine, and education. The goal is to help these people reach the first rung on the ladder of economic development so they can rise above mere subsistence level and achieve some control over their economic futures and their lives. To do this, Sachs proposes nine specific steps, which he explains in great detail in The End of Poverty. Though his plan certainly requires the help of rich nations, the financial assistance Sachs calls for is surprisingly modest--more than is now provided, but within the bounds of what has been promised in the past. For the U.S., for instance, it would mean raising foreign aid from just 0.14 percent of GNP to 0.7 percent. Sachs does not view such help as a handout but rather an investment in global economic growth that will add to the security of all nations. In presenting his argument, he offers a comprehensive education on global economics, including why globalization should be embraced rather than fought, why international institutions such as the United Nations, International Monetary Fund, and World Bank need to play a strong role in this effort, and the reasons why extreme poverty exists in the midst of great wealth. He also shatters some persistent myths about poor people and shows how developing nations can do more to help themselves.
The Amazon review provides an introduction:
Celebrated economist Jeffrey Sachs has a plan to eliminate extreme poverty around the world by 2025. If you think that is too ambitious or wildly unrealistic, you need to read this book. His focus is on the one billion poorest individuals around the world who are caught in a poverty trap of disease, physical isolation, environmental stress, political instability, and lack of access to capital, technology, medicine, and education. The goal is to help these people reach the first rung on the ladder of economic development so they can rise above mere subsistence level and achieve some control over their economic futures and their lives. To do this, Sachs proposes nine specific steps, which he explains in great detail in The End of Poverty. Though his plan certainly requires the help of rich nations, the financial assistance Sachs calls for is surprisingly modest--more than is now provided, but within the bounds of what has been promised in the past. For the U.S., for instance, it would mean raising foreign aid from just 0.14 percent of GNP to 0.7 percent. Sachs does not view such help as a handout but rather an investment in global economic growth that will add to the security of all nations. In presenting his argument, he offers a comprehensive education on global economics, including why globalization should be embraced rather than fought, why international institutions such as the United Nations, International Monetary Fund, and World Bank need to play a strong role in this effort, and the reasons why extreme poverty exists in the midst of great wealth. He also shatters some persistent myths about poor people and shows how developing nations can do more to help themselves.
The Good German
Peter Schjeldahl writes about Ernst Ludwig Kirchner’s 'Berlin Street Scene' (1913-14) + other viewpoints @ http://www.newyorker.com/arts/critics/notebook/2007/08/20/070820gonb_GOAT_notebook_schjeldahl
Disharmony In The Concert
David Alan Brown writes about the differences between the styles + the metamorphic poetry and evocative power of new type (s) of painting (s) by Titian and Giorgione + other viewpoints @ http://artnews.com/issues/article.asp?art_id=2081
Greatest Film Directors
1. Alfred Hitchcock
2. D.W. Griffith
3. Orson Welles
4. Jean-Luc Godard
5. John Ford
6. Stanley Kubrick
7. Sergei Eisenstein
8. Charlie Chaplin
9. Federico Fellini
10. Steven Spielberg
2. D.W. Griffith
3. Orson Welles
4. Jean-Luc Godard
5. John Ford
6. Stanley Kubrick
7. Sergei Eisenstein
8. Charlie Chaplin
9. Federico Fellini
10. Steven Spielberg
A Market Premium For Fraud
Chaim Even-Zohar writes about the side-effects of Certifigate scandal + the diamond dealer (s) concerns + the consumer (s) dilema + other viewpoints @ http://www.idexonline.com/portal_FullEditorial.asp?TextSearch=&KeyMatch=0&id=25232
Short Cuts To Certainty
(via The Australian Gemmologist, Vol.12. No.2, May 1974) B W Anderson writes:
Although in the case of rubies synthetic stones show a markedly brighter fluorescence under shortwave ultraviolet light than natural stones from Burma or Ceylon, it would be unwise to rely on this effect except perhaps as a means of indicating which stones in a large parcel should be picked out as samples for examination under microscope. In a laboratory where X-rays are available a surer distinction is provided by the prolonged red after-glow (phosphorescence) shown by synthetic rubies by whatever process these are manufactured, in contrast to the almost instantaneous extinction of the red glow in the case of natural rubies when the rays are cut off. Another useful indication where small extremely ‘clean’ synthetic rubies are concerned is afforded by placing these (in a dark room table) downwards on a sheet of slow printing paper in a flat bottomed dish, accompanied by natural Burma and synthetic rubies of similar size. Sufficient water should be added to cover the stones, and they should then be exposed for a few seconds to rays from a shortwave lamp held some two feet above the dish. The paper is then developed and, if the exposure has been correctly judged, the natural and synthetic rubies chosen as standards should show very clearly the much greater transparency of the synthetic rubies to the 2537 Å mercury radiation from the lamp, on which basis the origin of the ‘unknown’ stones under the test can be judged.
The popular type of synthetic corundum made to simulate alexandrite is usually easy to recognize by eye, and shows the curved growth lines clearly. Where there is any difficulty here, the narrow absorption line at 4750 Å in the blue forms a rapid confirmatory test.
Another useful ‘shortcut’ test between natural and synthetic stones is found in the case of red spinel. When natural red spinels are exposed to a powerful beam of blue, or longwave ultraviolet, light and the resultant red fluorescent glow is examined with the spectroscope the curious fluted series of fluorescence lines, giving an ‘organpipe’ appearance, is exceedingly distinctive and forms a complete proof that the stone is natural red spinel. Synthetic red spinels, though not common, have been made by the Verneuil and other processes, and also show a bright red fluorescence. But the spectroscope here reveals no organpipe structure but a strong line at 6850 Å with a fainter band on the shortwave side of it, giving very much the appearance of the ruby fluorescent spectrum, though the wavelengths of course are different.
Turning now to other uses of the spectroscope in providing a rapid and complete testing method, one may mention the case of white or blue or golden zircons, all of which have been heat treated in Bangkok or elsewhere. Unlike Ceylon zircons which are well-known to show a strong series of absorption bands, the lines from these heat treated stones are very narrow and faint may even be missed in transmitted light. But I have found that the strongest of the absorption lines, that a 6535 Å in the orange-red, can always be seen by internally reflected light, together with the weaker line at 6590 Å which is its companion, these two lines being completely diagnostic for zircon. This rapid test is particularly useful in confirming the presence of small rose-cut zircons simulating diamond in the surrounds of rings or brooches.
Amongst the many other distinctive absorption bands which provide valuable ‘shortcuts’ in testing, I should like to mention one other which we have found particularly useful. This I the narrow and intense band at 4370 Å in the violet which is seen in light reflected from jadeite. Though this can be seen most easily in pale green and mauve varieties of the mineral, it can also usually be detected in the better quality green jadeites if a strong enough beam of blue light is used, and the slit of the spectroscope slightly widened. Incidentally, bands in the red end of the spectrum provide the surest means of distinguishing stained from unstained green jadeite.
There are so many ways in which both the appearance of diamond and its properties are distinctive that a number of ‘shortcut’ tests must suggest themselves. But the enormous importance of diamond as a gemstone, its appearance in so many forms of jewelry, and also the never ending attempts to synthesize substances which resemble it in appearance make a knowledge of variety of definitive tests advisable.
Simplest of all, of course, is a properly conducted hardness test. A polished piece of synthetic corundum should always be at hand against which an edge or corner of a suspected diamond can be carefully but firmly applied. Diamond is the only stone, which will ‘bite’ on a sapphire surface. Any mark produced should be rubbed and examined with a lens.
Extreme transparency to X-rays is another attribute of diamond which it is useful and reliable in the experience of vantage of providing visible evidence when comparison stones of known varieties and of similar size are also shown on the same radiograph.
Another unique feature of diamond, however, can only be used in stones which have a rather strong blue fluorescence under longwave ultraviolet light, is the brief yellowish after-glow shown when the stone is removed from the rays. Some practice is needed in observing this interesting phenomenon. The eyes should be dark-adapted and the fluorescing stone, held in the cupped hands, should be removed swiftly from the rays and the eye applied at once to the small dark chamber formed by the hands. There are several gemstones which show a blue fluorescence, but of these only diamond shows a yellow after-glow.
If space allowed I could describe many further ‘shortcut’ tests for other varieties of precious stones, but those I have given above are undoubtedly amongst the most useful and reliable in the experience of myself and my colleagues in the laboratory of the London Chamber of Commerce. Most of them are already well-known, but some I hope will be new to readers and help to shorten their labors when faced with testing problems which have to be solved not only with certainty but with speed.
Although in the case of rubies synthetic stones show a markedly brighter fluorescence under shortwave ultraviolet light than natural stones from Burma or Ceylon, it would be unwise to rely on this effect except perhaps as a means of indicating which stones in a large parcel should be picked out as samples for examination under microscope. In a laboratory where X-rays are available a surer distinction is provided by the prolonged red after-glow (phosphorescence) shown by synthetic rubies by whatever process these are manufactured, in contrast to the almost instantaneous extinction of the red glow in the case of natural rubies when the rays are cut off. Another useful indication where small extremely ‘clean’ synthetic rubies are concerned is afforded by placing these (in a dark room table) downwards on a sheet of slow printing paper in a flat bottomed dish, accompanied by natural Burma and synthetic rubies of similar size. Sufficient water should be added to cover the stones, and they should then be exposed for a few seconds to rays from a shortwave lamp held some two feet above the dish. The paper is then developed and, if the exposure has been correctly judged, the natural and synthetic rubies chosen as standards should show very clearly the much greater transparency of the synthetic rubies to the 2537 Å mercury radiation from the lamp, on which basis the origin of the ‘unknown’ stones under the test can be judged.
The popular type of synthetic corundum made to simulate alexandrite is usually easy to recognize by eye, and shows the curved growth lines clearly. Where there is any difficulty here, the narrow absorption line at 4750 Å in the blue forms a rapid confirmatory test.
Another useful ‘shortcut’ test between natural and synthetic stones is found in the case of red spinel. When natural red spinels are exposed to a powerful beam of blue, or longwave ultraviolet, light and the resultant red fluorescent glow is examined with the spectroscope the curious fluted series of fluorescence lines, giving an ‘organpipe’ appearance, is exceedingly distinctive and forms a complete proof that the stone is natural red spinel. Synthetic red spinels, though not common, have been made by the Verneuil and other processes, and also show a bright red fluorescence. But the spectroscope here reveals no organpipe structure but a strong line at 6850 Å with a fainter band on the shortwave side of it, giving very much the appearance of the ruby fluorescent spectrum, though the wavelengths of course are different.
Turning now to other uses of the spectroscope in providing a rapid and complete testing method, one may mention the case of white or blue or golden zircons, all of which have been heat treated in Bangkok or elsewhere. Unlike Ceylon zircons which are well-known to show a strong series of absorption bands, the lines from these heat treated stones are very narrow and faint may even be missed in transmitted light. But I have found that the strongest of the absorption lines, that a 6535 Å in the orange-red, can always be seen by internally reflected light, together with the weaker line at 6590 Å which is its companion, these two lines being completely diagnostic for zircon. This rapid test is particularly useful in confirming the presence of small rose-cut zircons simulating diamond in the surrounds of rings or brooches.
Amongst the many other distinctive absorption bands which provide valuable ‘shortcuts’ in testing, I should like to mention one other which we have found particularly useful. This I the narrow and intense band at 4370 Å in the violet which is seen in light reflected from jadeite. Though this can be seen most easily in pale green and mauve varieties of the mineral, it can also usually be detected in the better quality green jadeites if a strong enough beam of blue light is used, and the slit of the spectroscope slightly widened. Incidentally, bands in the red end of the spectrum provide the surest means of distinguishing stained from unstained green jadeite.
There are so many ways in which both the appearance of diamond and its properties are distinctive that a number of ‘shortcut’ tests must suggest themselves. But the enormous importance of diamond as a gemstone, its appearance in so many forms of jewelry, and also the never ending attempts to synthesize substances which resemble it in appearance make a knowledge of variety of definitive tests advisable.
Simplest of all, of course, is a properly conducted hardness test. A polished piece of synthetic corundum should always be at hand against which an edge or corner of a suspected diamond can be carefully but firmly applied. Diamond is the only stone, which will ‘bite’ on a sapphire surface. Any mark produced should be rubbed and examined with a lens.
Extreme transparency to X-rays is another attribute of diamond which it is useful and reliable in the experience of vantage of providing visible evidence when comparison stones of known varieties and of similar size are also shown on the same radiograph.
Another unique feature of diamond, however, can only be used in stones which have a rather strong blue fluorescence under longwave ultraviolet light, is the brief yellowish after-glow shown when the stone is removed from the rays. Some practice is needed in observing this interesting phenomenon. The eyes should be dark-adapted and the fluorescing stone, held in the cupped hands, should be removed swiftly from the rays and the eye applied at once to the small dark chamber formed by the hands. There are several gemstones which show a blue fluorescence, but of these only diamond shows a yellow after-glow.
If space allowed I could describe many further ‘shortcut’ tests for other varieties of precious stones, but those I have given above are undoubtedly amongst the most useful and reliable in the experience of myself and my colleagues in the laboratory of the London Chamber of Commerce. Most of them are already well-known, but some I hope will be new to readers and help to shorten their labors when faced with testing problems which have to be solved not only with certainty but with speed.
Dioptase
Chemistry: Hydrous copper silicate
Crystal system: Trigonal
Color: Translucent to opaque; intense greenish blue
Hardness: 5
Cleavage: Perfect: 3 directions; Fracture: conchoidal to uneven.
Specific gravity: 3.28 – 3.35
Refractive index: 1.694 – 1.709; Uniaxial positive; 0.053
Luster: Vitreous.
Dispersion: High
Dichroism: -
Occurrence: Chile, Namibia, Russia, DR Congo, USA.
Notes
Attractive emerald green color; uncut crystal clusters may be set in jewelry; faceted, cabochon.
Crystal system: Trigonal
Color: Translucent to opaque; intense greenish blue
Hardness: 5
Cleavage: Perfect: 3 directions; Fracture: conchoidal to uneven.
Specific gravity: 3.28 – 3.35
Refractive index: 1.694 – 1.709; Uniaxial positive; 0.053
Luster: Vitreous.
Dispersion: High
Dichroism: -
Occurrence: Chile, Namibia, Russia, DR Congo, USA.
Notes
Attractive emerald green color; uncut crystal clusters may be set in jewelry; faceted, cabochon.
Wednesday, August 15, 2007
Can You Identify This Stone?
(via The Canadian Gemmologist, Vol.III, No.4, Spring, 1982) I should be called the gemstone of Ireland, except that country is not my home. I am found frequently in veins of calcite or in mica schist. I have a variable S.G; my dichroism is considered to be strong; my color is very important to my value, and my R.I is rather critical in separating me from my synthetic and imitation brothers. What am I?
Answer: Beryl, variety Emerald
Answer: Beryl, variety Emerald
On Dialogue
Good Books: (via Emergic) David Bohm's On Dialogue is on thought and dialogue in a new way. I never realized how different + inspirational the concept was till I tried it with friends. It's a good book.
David Bohm was a quantum physicist. But he also made contributions to a number of other fields. He developed a technique called Bohm Dialogue. According to Wikipedia:
Bohm Dialogue or Bohmian Dialogue is a form of free association conducted in groups, with no predefined purpose in mind besides mutual understanding and exploration of human thought. It aims to allow participants to examine their preconceptions, prejudices and patterns of thought. Bohm dialogue was developed by David Bohm, Donald Factor and Peter Garrett starting in 1983. Bohm published his views on dialogue in a series of papers between 1985 and 1991.
Bohm Dialogue (often referred to simply as Dialogue by its proponents) is conducted in groups of 20 to 40 people, who sit in a single circle. Participants "suspend" their thoughts, impulses and judgments instead of speaking from their usual point of view, they carefully analyse their thoughts. According to the proposal, Dialogue should not be confused with discussion or debate, which, says Bohm, suggests working towards a goal rather than simply exploring and learning.
David Bohm wrote:
In a dialogue, however, nobody is trying to win. Everybody wins if anybody wins. There is a different sort of spirit to it. In a dialogue, there is no attempt to gain points, or to make your particular view prevail. Rather, whenever any mistake is discovered on the part of anybody, everybody gains. Its a situation called win-win, whereas the other game is win-lose - if i win, you lose. But a dialogue is something more of a common participation, in which we are not playing a game against each other, but with each other. In dialogue, everybody wins dialogue is really aimed at going into the whole thought process and changing the way the thought process occurs collectively.
David Bohm was a quantum physicist. But he also made contributions to a number of other fields. He developed a technique called Bohm Dialogue. According to Wikipedia:
Bohm Dialogue or Bohmian Dialogue is a form of free association conducted in groups, with no predefined purpose in mind besides mutual understanding and exploration of human thought. It aims to allow participants to examine their preconceptions, prejudices and patterns of thought. Bohm dialogue was developed by David Bohm, Donald Factor and Peter Garrett starting in 1983. Bohm published his views on dialogue in a series of papers between 1985 and 1991.
Bohm Dialogue (often referred to simply as Dialogue by its proponents) is conducted in groups of 20 to 40 people, who sit in a single circle. Participants "suspend" their thoughts, impulses and judgments instead of speaking from their usual point of view, they carefully analyse their thoughts. According to the proposal, Dialogue should not be confused with discussion or debate, which, says Bohm, suggests working towards a goal rather than simply exploring and learning.
David Bohm wrote:
In a dialogue, however, nobody is trying to win. Everybody wins if anybody wins. There is a different sort of spirit to it. In a dialogue, there is no attempt to gain points, or to make your particular view prevail. Rather, whenever any mistake is discovered on the part of anybody, everybody gains. Its a situation called win-win, whereas the other game is win-lose - if i win, you lose. But a dialogue is something more of a common participation, in which we are not playing a game against each other, but with each other. In dialogue, everybody wins dialogue is really aimed at going into the whole thought process and changing the way the thought process occurs collectively.
Greatest Films
The films I like:
Bonnie and Clyde (1967)
Casablanca (1942)
Chinatown (1974)
Dr. Strangelove: or How I Learned to Stop Worrying and Love the Bomb (1964)
E.T. The Extra-Terrestrial (1982)
The Godfather, Parts I and II (1972, 1974)
Goodfellas (1990)
On the Waterfront (1954)
Lawrence of Arabia (1962)
Miller's Crossing (1990)
Bonnie and Clyde (1967)
Casablanca (1942)
Chinatown (1974)
Dr. Strangelove: or How I Learned to Stop Worrying and Love the Bomb (1964)
E.T. The Extra-Terrestrial (1982)
The Godfather, Parts I and II (1972, 1974)
Goodfellas (1990)
On the Waterfront (1954)
Lawrence of Arabia (1962)
Miller's Crossing (1990)
Show And Tell
Kelly Devine Thomas writes about Louise Bourgeois's art + the artist's unique way of connecting with the world + other viewpoints @ http://artnews.com/issues/article.asp?art_id=2060
Dresden's World-Class Art Gallery Duplicates Itself Online
Andrew Curry writes about the virtual version of Dresden's World-Class Art Gallery via Second Life + other viewpoints @ http://www.wired.com/culture/art/multimedia/2007/08/gallery_dresden
Joining The Class
Chaim Even-Zohar writes about specific consumer class actions for illegal overpricing of diamonds against the key players in industry + other viewpoints @ http://www.idexonline.com/portal_FullEditorial.asp?TextSearch=&KeyMatch=0&id=25267
Short Cuts To Certainty
2007: B W Anderson is a giant in gemology. This is an excellent article for students, gem traders, lab gemologists and consumers. The methodology is simple and straightforward. Many in the trade do not understand lab gemologist's problems. The trade and consumers want quick results; they want lab gemologists to make god-like statements. To detect intruders in a mixed parcel of colored stones requires insight, knowledge, analytical skills and speed. This skill will come only with discipline, experience and guerilla concentration. Today's gemologists will have to be familiar with new synthetics, treated stones, and a variety of simulants very different from the 1970s.
(via The Australian Gemmologist, Vol.12. No.2, May 1974) B W Anderson writes:
The procedure when testing gemstones in a busy trade laboratory, such as that in which I spent all my professional life, must of necessity differ radically from the adopted by a student. And this difference does not depend so much on the apparatus available as upon the purpose of the exercise. The student’s chief task is to learn; the professional’s task is, above all, to identify.
For the student it is both interesting and advisable to study each specimen in an orderly and planned manner, beginning in most cases with the determination of its refractive indices on the refractometer, and continuing with a study of its inclusions under the microscope, its absorption of light by means of the spectroscope, its dichroism, and so on. There may even be time for an accurate determination of its specific gravity. By doing all this, the young gemologist becomes accustomed to handling all his instruments, and gradually learns from first-hand the properties of each gem variety. The values he measures cease to be figures in a textbook and become recognized as living attributes of the stones concerned. If his teacher is wise he will also become trained in the intelligent use of a 10x lens, which alone can be his constant companion outside the laboratory, and with which so many gemological decisions can be made without resort to more elaborate instruments.
For the laboratory gemologists, while the first essential is of an accurate appraisal of each specimen, the next and pressing necessity is for speed. Once he has achieved a conclusive result he may have to deny himself the pleasure of further examining a stone in all its fascinating aspects, and after completing his report, must pass on to the next test. So often it seems that his client is waiting to known his decision before signing a cheque to conclude a deal.
There will usually be a wide choice of test available, but, after careful preliminary inspection (which in itself may prove conclusive) the expert must decide which test or tests will provide him with a specific answer. Since commercial gem testing so often consists in distinguishing between natural and synthetic stones, the refractometer is seldom needed, which is just as well as, however carefully handled, the soft glass of that instrument soon becomes marred by scratches and must then be repolished. A refractometer on which 1000 stones have been tested will certainly need repair while, in contrast, a micrometer or spectroscope through which a hundred times that number have been examined will have suffered no ill effects.
The nature of the goods will often dictate the first step in testing quite clearly. For example, where hundreds of small rubies are submitted it will be a valid assumption that the stones are all red corundums, the point at issue being whether they are natural or synthetic. The gemologist will therefore turn first to the microscope, knowing that in the course of examination of the stones under magnification he will, as an experienced gemologist, be able to satisfy himself as to both the origin and the species. Initially the stones can be examined in the dry state suitably distributed in lines on a glass plate. Any stones which do not at once show distinctive features can be put on one side for more thorough examination, either under oil immersion or by alternative methods.
To take another instance—a parcel of stones purporting to be tourmalines. In this case the stones would clearly be destined for a refractometer test, since here the microscope would of little value since there are (thank goodness) no synthetic tourmalines yet available, and refractive index and birefringence measurements will provide the definite answer required. In passing, one may remark that in testing such stones as tourmaline, quartz or beryl, which have a low R.I, it is very advantageous to use a Rayner ‘spinel’ refractometer, since this gives easy readings to three places of decimals in ordinary white light and suffers hardly any mechanical damage.
It is much difficult to decide a plan of action where a large parcel of mixed stones is to be tested, or a brooch or necklace set with a variety of stones, as each species may well need a different approach, and it is tedious and time consuming to be moving constantly from one instrument to another. In the case of a large parcel of mixed stones it may indeed be worth while to begin by sorting the stones by eye into groups which appear to be of the same type, after which the determination of each group will be far more rapid. Where the majority of stones in a parcel or group are all of one kind there are several ways in which any ‘intruders’ may be rapidly detected. For example, when in a parcel of yellow topaz stones some citrines have intruded, a flotation test in a bromoform solution will quickly separate them, and another useful technique is to make plain any differences in refractive index by immersion in a suitable liquid. One such case was clearly demonstrated when a contact photograph was made of a necklace consisting mainly of colored tourmaline beads. In this case the necklace was immersed in bromobenzene (R.I=1.56) in a glass dish under which a slow photographic film was placed in a dark room and exposed for a few seconds to an overhead light. The print from the developed film showed clearly a thick dark outline in each of the tourmaline beads indicating that their R.I was well above 1.56, whereas the five aquamarines which were mixed in with the tourmalines nearly matched the liquid in R.I and showed hardly any outline, making them very easy to distinguish.
Sometimes the detection of ‘intruders’ may be accomplished in a quite unorthodox manner. I can remember when some 30 years ago I had to test a packet of 117 small green stones, labeled ‘dark olivines’, which a preliminary inspection revealed as being mainly demantoid garnets. Here the most rapid and positive test proved to be examination under a low power microscope. I had recently become aware of the prevalence of ‘horsetail’ asbestos fibres as an almost inevitable inclusion in demantoid garnets, and was delighted to see these most characteristic features in all but seven of the stones. These seven were then examined with a spectroscope, which enabled me to complete the test in a very short time. One stone was a ‘clean’ demantoid, two were peridots, one a green sapphire, and three were green andalusites from Brazil of that kind which show delicate absorption bands due to manganese.
Of course, even an experienced gemologist may choose a wrong approach to a problem, and is annoyed to feel that he has wasted too much time in completing a test. Mathematicians have a word for the proof of a problem which is not only sound but also rapid and incisive. They speak of such as an ‘elegant’ proof. And it is an ‘elegant’ proof that a good gemologist would always wish to choose, and which gives him real satisfaction as a craftsman and as a scientist.
In the interests of time-saving the experienced gemologist is glad to take advantage of certain features which he knows to be unique to one species or one variety of gemstone. Particularly valuable are those tests which not only determine the species of gemstone, but at the same time prove it to be natural or synthetic in origin. Such are ‘shortcuts to certainty’ referred to in the title of this article, and I will now proceed to give details of some of these which have proved of particular value in the London laboratory.
First in importance I would undoubtedly place the group of absorption bands in the blue part of the spectrum (in particular the strongest of these, at 4500 Å) which can be seen in natural sapphires. Since C J Payne and I first observed this band in 1933 we have noted its presence in many thousands of natural sapphires but never in any faceted synthetic sapphire. We thus came to regard the presence of the 4500 Å band as a valuable and undeniably proof that the stone concerned was a natural sapphire (though nowadays the possibility of a doublet consisting in part of natural sapphire must be borne in mind). The band also indicates that geographical origin of the stone to some extent, according to the content of Fe2O3 typical for each locality. Thus while Ceylon sapphires may show only a single faint and narrow band at 4500 Å, Australian stones and green sapphires show a strong and broad absorption block within which the three main bands at 4500, 4600 and 4710 Å can be discerned. Sapphires from other localities, arranged in order or increasing absorption strength, can be written thus: Burma, Kashmir, Siam, Kenya, Montana. In cases where the band is almost invisibly weak, as is often true of Ceylon stones, it is wise to confirm it by wavelength measurement to ensure that the supposed band is not a matter of imagination or wishful thinking. The Beck ‘wavelength’ spectroscope is admirable for this purpose, since the crosswires in the eyepiece can be made to traverse the spectrum by rotating a drum marked in supposed band without the observer knowing what the reading is until he looks at the scale on the drum.
Observation is greatly assisted in this part of the spectrum if the light is filtered through a flask containing strong copper sulphate solution, and, since the 4500 Å band is an ‘ordinary’ ray phenomenon, a Polaroid disc may also serve to emphasize the reality of its presence.
The 4500 Å complex is also useful in confirming that yellow sapphires from Siam (Thailand) or Australia are not synthetic corundums, as these show the bands quite strongly. In yellow sapphires from Ceylon the band is seldom visible, but here an apricot-colored fluorescence under longwave ultraviolet light is a helpful sign (as well, of course, as the inclusions which are usually present).
Looking at the problem from the synthetic side, the common reaction of synthetic blue sapphires to shortwave ultraviolet light is to show a curious whitish or greenish surface fluorescence which is so weak that it needs a darkened room and dark-adapted eyes for its observation. Since natural Ceylon sapphires have on rare occasions been known to show a similar stringent one by examining the surface of the fluorescing stone, since this frequently reveals curved structure lines, even when these are hard to see in ordinary light.
The wise gemologist will not supersede the conventional examination of sapphires under lens or microscope, which in themselves often enable him to make a sure and quick decision, but they can be enormously helpful in providing proof in the case of ‘clean’ stones showing no easily observable structures.
Short Cuts To Certainty (continued)
(via The Australian Gemmologist, Vol.12. No.2, May 1974) B W Anderson writes:
The procedure when testing gemstones in a busy trade laboratory, such as that in which I spent all my professional life, must of necessity differ radically from the adopted by a student. And this difference does not depend so much on the apparatus available as upon the purpose of the exercise. The student’s chief task is to learn; the professional’s task is, above all, to identify.
For the student it is both interesting and advisable to study each specimen in an orderly and planned manner, beginning in most cases with the determination of its refractive indices on the refractometer, and continuing with a study of its inclusions under the microscope, its absorption of light by means of the spectroscope, its dichroism, and so on. There may even be time for an accurate determination of its specific gravity. By doing all this, the young gemologist becomes accustomed to handling all his instruments, and gradually learns from first-hand the properties of each gem variety. The values he measures cease to be figures in a textbook and become recognized as living attributes of the stones concerned. If his teacher is wise he will also become trained in the intelligent use of a 10x lens, which alone can be his constant companion outside the laboratory, and with which so many gemological decisions can be made without resort to more elaborate instruments.
For the laboratory gemologists, while the first essential is of an accurate appraisal of each specimen, the next and pressing necessity is for speed. Once he has achieved a conclusive result he may have to deny himself the pleasure of further examining a stone in all its fascinating aspects, and after completing his report, must pass on to the next test. So often it seems that his client is waiting to known his decision before signing a cheque to conclude a deal.
There will usually be a wide choice of test available, but, after careful preliminary inspection (which in itself may prove conclusive) the expert must decide which test or tests will provide him with a specific answer. Since commercial gem testing so often consists in distinguishing between natural and synthetic stones, the refractometer is seldom needed, which is just as well as, however carefully handled, the soft glass of that instrument soon becomes marred by scratches and must then be repolished. A refractometer on which 1000 stones have been tested will certainly need repair while, in contrast, a micrometer or spectroscope through which a hundred times that number have been examined will have suffered no ill effects.
The nature of the goods will often dictate the first step in testing quite clearly. For example, where hundreds of small rubies are submitted it will be a valid assumption that the stones are all red corundums, the point at issue being whether they are natural or synthetic. The gemologist will therefore turn first to the microscope, knowing that in the course of examination of the stones under magnification he will, as an experienced gemologist, be able to satisfy himself as to both the origin and the species. Initially the stones can be examined in the dry state suitably distributed in lines on a glass plate. Any stones which do not at once show distinctive features can be put on one side for more thorough examination, either under oil immersion or by alternative methods.
To take another instance—a parcel of stones purporting to be tourmalines. In this case the stones would clearly be destined for a refractometer test, since here the microscope would of little value since there are (thank goodness) no synthetic tourmalines yet available, and refractive index and birefringence measurements will provide the definite answer required. In passing, one may remark that in testing such stones as tourmaline, quartz or beryl, which have a low R.I, it is very advantageous to use a Rayner ‘spinel’ refractometer, since this gives easy readings to three places of decimals in ordinary white light and suffers hardly any mechanical damage.
It is much difficult to decide a plan of action where a large parcel of mixed stones is to be tested, or a brooch or necklace set with a variety of stones, as each species may well need a different approach, and it is tedious and time consuming to be moving constantly from one instrument to another. In the case of a large parcel of mixed stones it may indeed be worth while to begin by sorting the stones by eye into groups which appear to be of the same type, after which the determination of each group will be far more rapid. Where the majority of stones in a parcel or group are all of one kind there are several ways in which any ‘intruders’ may be rapidly detected. For example, when in a parcel of yellow topaz stones some citrines have intruded, a flotation test in a bromoform solution will quickly separate them, and another useful technique is to make plain any differences in refractive index by immersion in a suitable liquid. One such case was clearly demonstrated when a contact photograph was made of a necklace consisting mainly of colored tourmaline beads. In this case the necklace was immersed in bromobenzene (R.I=1.56) in a glass dish under which a slow photographic film was placed in a dark room and exposed for a few seconds to an overhead light. The print from the developed film showed clearly a thick dark outline in each of the tourmaline beads indicating that their R.I was well above 1.56, whereas the five aquamarines which were mixed in with the tourmalines nearly matched the liquid in R.I and showed hardly any outline, making them very easy to distinguish.
Sometimes the detection of ‘intruders’ may be accomplished in a quite unorthodox manner. I can remember when some 30 years ago I had to test a packet of 117 small green stones, labeled ‘dark olivines’, which a preliminary inspection revealed as being mainly demantoid garnets. Here the most rapid and positive test proved to be examination under a low power microscope. I had recently become aware of the prevalence of ‘horsetail’ asbestos fibres as an almost inevitable inclusion in demantoid garnets, and was delighted to see these most characteristic features in all but seven of the stones. These seven were then examined with a spectroscope, which enabled me to complete the test in a very short time. One stone was a ‘clean’ demantoid, two were peridots, one a green sapphire, and three were green andalusites from Brazil of that kind which show delicate absorption bands due to manganese.
Of course, even an experienced gemologist may choose a wrong approach to a problem, and is annoyed to feel that he has wasted too much time in completing a test. Mathematicians have a word for the proof of a problem which is not only sound but also rapid and incisive. They speak of such as an ‘elegant’ proof. And it is an ‘elegant’ proof that a good gemologist would always wish to choose, and which gives him real satisfaction as a craftsman and as a scientist.
In the interests of time-saving the experienced gemologist is glad to take advantage of certain features which he knows to be unique to one species or one variety of gemstone. Particularly valuable are those tests which not only determine the species of gemstone, but at the same time prove it to be natural or synthetic in origin. Such are ‘shortcuts to certainty’ referred to in the title of this article, and I will now proceed to give details of some of these which have proved of particular value in the London laboratory.
First in importance I would undoubtedly place the group of absorption bands in the blue part of the spectrum (in particular the strongest of these, at 4500 Å) which can be seen in natural sapphires. Since C J Payne and I first observed this band in 1933 we have noted its presence in many thousands of natural sapphires but never in any faceted synthetic sapphire. We thus came to regard the presence of the 4500 Å band as a valuable and undeniably proof that the stone concerned was a natural sapphire (though nowadays the possibility of a doublet consisting in part of natural sapphire must be borne in mind). The band also indicates that geographical origin of the stone to some extent, according to the content of Fe2O3 typical for each locality. Thus while Ceylon sapphires may show only a single faint and narrow band at 4500 Å, Australian stones and green sapphires show a strong and broad absorption block within which the three main bands at 4500, 4600 and 4710 Å can be discerned. Sapphires from other localities, arranged in order or increasing absorption strength, can be written thus: Burma, Kashmir, Siam, Kenya, Montana. In cases where the band is almost invisibly weak, as is often true of Ceylon stones, it is wise to confirm it by wavelength measurement to ensure that the supposed band is not a matter of imagination or wishful thinking. The Beck ‘wavelength’ spectroscope is admirable for this purpose, since the crosswires in the eyepiece can be made to traverse the spectrum by rotating a drum marked in supposed band without the observer knowing what the reading is until he looks at the scale on the drum.
Observation is greatly assisted in this part of the spectrum if the light is filtered through a flask containing strong copper sulphate solution, and, since the 4500 Å band is an ‘ordinary’ ray phenomenon, a Polaroid disc may also serve to emphasize the reality of its presence.
The 4500 Å complex is also useful in confirming that yellow sapphires from Siam (Thailand) or Australia are not synthetic corundums, as these show the bands quite strongly. In yellow sapphires from Ceylon the band is seldom visible, but here an apricot-colored fluorescence under longwave ultraviolet light is a helpful sign (as well, of course, as the inclusions which are usually present).
Looking at the problem from the synthetic side, the common reaction of synthetic blue sapphires to shortwave ultraviolet light is to show a curious whitish or greenish surface fluorescence which is so weak that it needs a darkened room and dark-adapted eyes for its observation. Since natural Ceylon sapphires have on rare occasions been known to show a similar stringent one by examining the surface of the fluorescing stone, since this frequently reveals curved structure lines, even when these are hard to see in ordinary light.
The wise gemologist will not supersede the conventional examination of sapphires under lens or microscope, which in themselves often enable him to make a sure and quick decision, but they can be enormously helpful in providing proof in the case of ‘clean’ stones showing no easily observable structures.
Short Cuts To Certainty (continued)
Variscite
(Utahlite)
Chemistry: Hydrous aluminum iron phosphate; amarice with quartz.
Crystal system: Orthorhombic; massive as nodules, cavity fillers and crusts.
Color: Semi translucent to opaque; yellow green, bluish green, greenish blue; specimens contain brownish yellow to greenish yellow matrix.
Hardness: 5
Cleavage: Perfect: 1 direction; Fracture: brittle, conchoidal.
Specific gravity: 2.55 (2.52- 2.6)
Refractive index: 1.56 mean (1.56-1.59); biaxial negative.
Luster: Massive: vitreous, dull.
Dispersion:-
Dichroism: -
Occurrence: Sedimentary (by direct deposition from phosphate-bearing water that has reacted with aluminum rich rocks in near surface environments); Australia, USA.
Notes
Sometimes called Utahlite from its USA occurrence; may look like turquoise but hardness and SG lower; spectrum: strong line at 688nm, weak line at 650nm, not diagnostic; cabochons, carvings.
Chemistry: Hydrous aluminum iron phosphate; amarice with quartz.
Crystal system: Orthorhombic; massive as nodules, cavity fillers and crusts.
Color: Semi translucent to opaque; yellow green, bluish green, greenish blue; specimens contain brownish yellow to greenish yellow matrix.
Hardness: 5
Cleavage: Perfect: 1 direction; Fracture: brittle, conchoidal.
Specific gravity: 2.55 (2.52- 2.6)
Refractive index: 1.56 mean (1.56-1.59); biaxial negative.
Luster: Massive: vitreous, dull.
Dispersion:-
Dichroism: -
Occurrence: Sedimentary (by direct deposition from phosphate-bearing water that has reacted with aluminum rich rocks in near surface environments); Australia, USA.
Notes
Sometimes called Utahlite from its USA occurrence; may look like turquoise but hardness and SG lower; spectrum: strong line at 688nm, weak line at 650nm, not diagnostic; cabochons, carvings.
Tuesday, August 14, 2007
Can You Identify This Stone?
(via The Canadian Gemmologist, Vol.III, No.3, Spring, 1982) . I am quite new as a faceted gemstone. I have been known for a long time as massive material, but only recently did they discover me in transparent crystals. I am strongly pleochroic, and crystallize in orthorhombic prisms. If I were a bit harder, I could pass muster as one of the so-called ‘precious’ gemstones. But my hardness of 6½ does not mean that I am cheap. What am I?
Answer: Zoisite, variety Tanzanite
Answer: Zoisite, variety Tanzanite
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