(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.
Tuesday, April 17, 2007
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.
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