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Thulite (sometimes called rosaline) is an opaque, massive pink manganese-bearing variety of the mineral zoisite. Manganese substitutes for calcium in the structure with up to two percent Mn2+. Thulite is often mottled with white calcite and occurs as veins and fracture fillings transecting many types of rock. In mineralogical literature, thulite may sometimes refer to any pink zoisite. Clinothulite is the manganese bearing variety of monoclinic clinozoisite.

Thulite was first discovered at a place called Sauland in Telemark, Norway in 1820. It is named after the mythical island of Thule in the belief that the island is Norway. Thulite is used as a gemstone and carving material in the manufacture of jewellery and ornamental objects.

Thulite is also found in the Austrian Tyrol, in Mitchell County, North Carolina, and in Western Australia. A new, more recent find of high quality thulite was discovered near Riverside in Okanogan County, Washington, USA.

Thulite Properties

Chemical Composition: 
Silicate of calcium and aluminium - Ca2(Al,OH)Al2(SiO4)3
Classification / Type: 
Belongs to the epidote group of minerals.
Colors / Varieties: 
Pink
Crystal System / Forms: 
Orthorhombic System
Hardness: 
6
Specific Gravity: 
3.09 - 3.12
Cleavage / Fracture: 
Perfect 1 directional cleavage / Conchoidal fracture.
Optic Character: 
Anisotropic, D.R.; Biaxial positive.
Lustre: 
Vitreous
Refractive Index / Birefringence: 
1.691 - 1.700 / 0.009; Range: 1.688 - 1.707
Pleochroism: 
Weak
Dispersion: 
0.021
Magnification: 
Parallel fibrous canals, crystals, fingerprints.
U.V. Fluorescence: 
Weak orange yellow in longwave.
Cause of Color: 
Manganese
Treatment (Enhancement): 
Colorless impregnation: With oil or resin to improve clarity.
Simulants (with separation tests): 
Synthetic Sapphire (optic figure, R.I., S.G., inclusions), Synthetic Spinel (optic character), Synthetic Quartz (optic figure, R.I., S.G., pleochroism), Iolite (R.I., S.G., pleochroism), Glass (optic character), Tourmaline (optic figure, R.I., birefringence), Rough Smoky Quartz (S.G., pleochroism)
Geological Occurrence: 
In metamorphic rocks subjected to regional metamorphism.
Sources: 
U.S.A. (North Carolina), Australia.
Cuts & Uses: 
Facetted cuts, cabochon, carving, etc.
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Tanzanite is the blue/purple variety of the mineral zoisite (a calcium aluminium hydroxy silicate) which was discovered in the Mererani Hills of Northern Tanzania in 1967, near the city of Arusha and Mount Kilimanjaro. It is used as a gemstone. Tanzanite is noted for its remarkably strong trichroism, appearing alternately sapphire blue, violet and burgundy depending on crystal orientation. Tanzanite can also appear differently when viewed under alternate lighting conditions.

The blues appear more evident when subjected to fluorescent light and the violet hues can be seen readily when viewed under incandescent illumination. Tanzanite in its rough state is usually a reddish brown color. It requires artificial heat treatment to 600 °C in a gemological oven to bring out the blue violet of the stone. Tanzanite is a rare gem. It is found mostly in the foothills of Mount Kilimanjaro. The mineral is named after Tanzania, the country in which it was discovered.

Tanzanite Properties

Chemical Composition: 
Silicate of calcium and aluminium - Ca2(Al,OH)Al2(SiO4)3
Classification / Type: 
Belongs to the epidote group of minerals.
Colors / Varieties: 
Blue
Crystal System / Forms: 
Orthorhombic System
Hardness: 
6
Specific Gravity: 
3.15 - 3.38
Cleavage / Fracture: 
Perfect 1 directional cleavage / Conchoidal fracture.
Optic Character: 
Anisotropic, D.R.; Biaxial positive.
Lustre: 
Vitreous
Refractive Index / Birefringence: 
1.691 - 1.700 / 0.009; Range: 1.688 - 1.707
Pleochroism: 
Deep blue / purple / pink; or, reddish purple / blue / yellowish brown
Dispersion: 
0.021
Magnification: 
Parallel fibrous canals, crystals, fingerprints.
U.V. Fluorescence: 
Inert.
Spectrum: 
Absorption centered at 595nm
Cause of Color: 
Vanadium
Treatment (Enhancement): 
  • Colored impregnation: Blue color is introduced into fractures to improve color.
  • Heat treatment: Commonly brownish blue stones are heated to produce the deep blue of tanzanite. The intensity of the starting color decides the percentage of the color change.
Specific Tests: 
Strong pleochroism
Simulants (with separation tests): 
  • Synthetic Forsterite: Strong pleochroism (similar to tanzanite), R.I. 1.635 - 1.670, strong doubling, dotted gas bubbles.
  • Synthetic Blue Sapphire (optic figure, R.I., S.G., inclusions), Synthetic Spinel (optic character), Synthetic Quartz (optic figure, R.I., S.G., pleochroism), Iolite (R.I., S.G., pleochroism), Glass (optic character), Tourmaline (optic figure, R.I., birefringence), Rough Smoky Quartz (S.G., pleochroism)
Geological Occurrence: 
In metamorphic rocks subjected to regional metamorphism.
Sources: 
Tanzania
Cuts & Uses: 
Facetted cuts, cabochon, carving, etc.
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Zoisite occurs in a number of varieties, the most sought-after being tanzanite, a variety colored sapphire-blue by the presence of vanadium. Tanzanite crystals have distinct pleochriosm, showing either purple, blue or slate-grey depending on the angle they are viewed from. There may also be a slight color change in incandescent light (such as that from a light blub), when stones may appear more violet. A massive green variety of zoisite, containing rubies and occasionally dark horn-blende inclusions, may be polished, carved, or tumbled to make ornaments or an attractive decorative stone. Thulite, a massive, pinkish red variety colored by manganese, is also polished or carved to make small ornaments. Tanzanite has been confused with sapphire, and thulite with rhodonite. Some heating of zoisite varieties may enhance their colour.

Tanzanite was first found in Tanzania (hence the name). Yellow and green zoisite occurs in Tanzania and Kenya. Thulite is found in Norway, Austria, western Australia, Italy and North Carolina (USA).

Discovered by Baron von Zois in the Sau-Alp mountains of Austria, zoisite was first called saualpite.

Zoisite Properties

Chemical Composition: 
Silicate of calcium and aluminium - Ca2(Al,OH)Al2(SiO4)3
Classification / Type: 
Belongs to the epidote group of minerals.
Colors / Varieties: 
  • Blue - Tanzanite
  • Pink - Thulite
  • Green, yellow, brown, violet
  • Chatoyant varieties
Crystal System / Forms: 
Orthorhombic System / Prismatic or tabular crystals, often striated, Also massive.
Hardness: 
6
Cleavage / Fracture: 
Perfect 1 directional cleavage / Conchoidal fracture.
Optic Character: 
Anisotropic, D.R.; Biaxial positive.
Lustre: 
Vitreous
Refractive Index / Birefringence: 
1.691 - 1.700 / 0.009; Range: 1.688 - 1.707
Dispersion: 
0.021
Magnification: 
Parallel fibrous canals, crystals, fingerprints.
U.V. Fluorescence: 
Inert.
Cause of Color: 
Green - Chromium
Treatment (Enhancement): 
Colorless impregnation: With oil or resin to improve clarity.
Simulants (with separation tests): 
Synthetic Sapphire (optic figure, R.I., S.G., inclusions), Synthetic Spinel (optic character), Synthetic Quartz (optic figure, R.I., S.G., pleochroism), Iolite (R.I., S.G., pleochroism), Glass (optic character), Tourmaline (optic figure, R.I., birefringence), Rough Smoky Quartz (S.G., pleochroism)
Geological Occurrence: 
In metamorphic rocks subjected to regional metamorphism.
Sources: 
Tanzania, U.S.A. (North Carolina), Australia.
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Zoisite occurs in a number of varieties, the most sought-after being tanzanite, a variety colored sapphire-blue by the presence of vanadium. Tanzanite crystals have distinct pleochriosm, showing either purple, blue or slate-grey depending on the angle they are viewed from. There may also be a slight color change in incandescent light (such as that from a light blub), when stones may appear more violet. A massive green variety of zoisite, containing rubies and occasionally dark horn-blende inclusions, may be polished, carved, or tumbled to make ornaments or an attractive decorative stone. Thulite, a massive, pinkish red variety colored by manganese, is also polished or carved to make small ornaments. Tanzanite has been confused with sapphire, and thulite with rhodonite. Some heating of zoisite varieties may enhance their colour.

Tanzanite was first found in Tanzania (hence the name). Yellow and green zoisite occurs in Tanzania and Kenya. Thulite is found in Norway, Austria, western Australia, Italy and North Carolina (USA).

Discovered by Baron von Zois in the Sau-Alp mountains of Austria, zoisite was first called saualpite.

Zoisite Properties

Chemical Composition: 
Silicate of calcium and aluminium - Ca2(Al,OH)Al2(SiO4)3
Classification / Type: 
Belongs to the epidote group of minerals.
Colors / Varieties: 
  • Blue - Tanzanite
  • Pink - Thulite
  • Green, yellow, brown, violet
  • Chatoyant varieties
Crystal System / Forms: 
Orthorhombic System / Prismatic or tabular crystals, often striated, Also massive.
Hardness: 
6
Cleavage / Fracture: 
Perfect 1 directional cleavage / Conchoidal fracture.
Optic Character: 
Anisotropic, D.R.; Biaxial positive.
Lustre: 
Vitreous
Refractive Index / Birefringence: 
1.691 - 1.700 / 0.009; Range: 1.688 - 1.707
Dispersion: 
0.021
Magnification: 
Parallel fibrous canals, crystals, fingerprints.
U.V. Fluorescence: 
Inert.
Cause of Color: 
Green - Chromium
Treatment (Enhancement): 
Colorless impregnation: With oil or resin to improve clarity.
Simulants (with separation tests): 
Synthetic Sapphire (optic figure, R.I., S.G., inclusions), Synthetic Spinel (optic character), Synthetic Quartz (optic figure, R.I., S.G., pleochroism), Iolite (R.I., S.G., pleochroism), Glass (optic character), Tourmaline (optic figure, R.I., birefringence), Rough Smoky Quartz (S.G., pleochroism)
Geological Occurrence: 
In metamorphic rocks subjected to regional metamorphism.
Sources: 
Tanzania, U.S.A. (North Carolina), Australia.
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Zircon is most famous for its colorless stones, which closely resemble diamonds and have been used both intentionally and mistakenly in their place. Although colorless when pure, impurities will produce yellow, orange, blue, red, brown and green varieties. Brown stones from Thailand, Vietnam and Kampuchea are usually heat-treated to change them into the colorless or blue stones popular in jewelery. Blue stones that revert to brown will regain the blue if reheated. Blue zircon reheated in the presence of oxygen will change to golden-yellow. Zircon may be distinguished from diamond by its double refraction and by wear and tear on its facet edges. It has been imitated by both colorless glass and synthetic spinel. Some zircon contains radioactive thorium and uranium, which eventually break down the crystal structure. Decayed stones are known as “low” zircon, with a “metamict” structure; undamaged material is “high” zircon.

Gem-quality crystals are usually found as pebbles in alluvial deposits. Sri Lanka has been a source of gem material for over 2,000 years; other localities include Burma, Thailand, Cambodia, Vietnam, Kampuchea, Australia, Brazil, Nigeria, Tanzania, and France.

Zircon was believed to provide the wearer with wisdom, honor, and riches and loss of lustre was said to warn of danger. The name is from the Arabic zargun, which derives from the Persian for “gold color”.

Zircon Properties

Chemical Composition: 
Silicate of Zirconium with traces of Uranium and Thorium - ZrSiO4
Classification / Type: 
Classified into 3 categories - high, medium and low type. The presence of radioactive elements within the structure may cause the breakdown of the internal structure (metamictization). The extent of breakdown defines the three types.
Colors / Varieties: 
  • High Type: Blue, white, reddish brown
  • Medium Type:
  • Low Type: Green, Brown, Yellow (Metamict Zircon)
  • Chatoyant Varieties
Crystal System / Forms: 
Tetragonal System / Prismatic habit and also as water-worn pebbles. Tetragonal prisms with pyramidal and / or pinacoidal terminations.
Hardness: 
6.5 - 7.5 (low to high type)
Specific Gravity: 
  • High: 4.70
  • Medium: 4.32
  • Low: 4.00
Cleavage / Fracture: 
None / Conchoidal fracture.
Optic Character: 
Anisotropic, D.R.; Uniaxial Positive. Low type metamict zircon maybe almost amorphous.
Lustre: 
Adamantine to vitreous.
Refractive Index / Birefringence: 
  • High: 1.925 - 1.984 / 0.059
  • Medium: 1.875 - 1.945 / 0.006 - 0.050
  • Low: 1.810 - 1.815 / 0.002 - 0.005
Pleochroism: 
Variable dichroism with blue zircon showing the strongest effect.
Dispersion: 
Weak to Moderate. Maximum: 0.038
Magnification: 
Angular zoning and streaks (are sometimes seen in low type), crystals, doubling of facet edges, abraded facet edges.
U.V. Fluorescence: 
Variable, commonly mustard yellow in shortwave and dull yellow in longwave. It may phosphoresce also.
Spectrum: 
  • The strongest line is at 653.5nm due to Uranium.
  • Many narrow lines and strong bands across the whole spectrum, ranging from more than 40 lines (in Myanmar Zircon) to only a few lines (in Australian Zircon). Other lines are 653.5nm, 691.0nm, 683.0nm, 662.5nm, 660.5nm, 621.0nm, 615.0nm, 589.5nm, 562.5nm, 537.5nm, 516.0nm, 484.0nm, 460.0nm, 432.7nm
  • Heat treated and low type zircon has a weak spectrum.
  • Colorless, blue and golden brown (all heat treated) zircons exhibit one fine line at 653.5nm
  • Some of zircons may display no spectrum at all.
Cause of Color: 
Color centers.
Treatment (Enhancement): 
Heating brown to red, yellow, colorless and blue.
Specific Tests: 
Metamict Zircon: Low type zircons in which the internal structure is broken down due to residual radioactive decay. Though doubly refracting, they become almost singly refracting. Their properties are lower (R.I., S.G.) and they may exhibit weak doubling.
Simulants (with separation tests): 
Sphene (optic figure, dispersion, spectrum), Synthetic Cubic Zirconia (optic character, dispersion, spectrum), Y.A.G. (optic character, spectrum), G.G.G. (optic character, spectrum, S.G.), Strontium Titanate (optic character, S.G. dispersion), Diamond (optic character, S.G., spectrum), Demantoid (optic character, spectrum, inclusions), Malaya Garnet (optic character, S.G., spectrum), Topaz (R.I., S.G., spectrum, dispersion), Natural / Synthetic Sapphire (R.I., spectrum, doubling), etc.
Geological Occurrence: 
In igneous rocks and alluvial deposits.
Sources: 
Sri Lanka, Myanmar, Thailand, Cambodia, France, India, Australia, Madagascar.
Cuts & Uses: 
Facetted cuts, cabochons, beads, etc.
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Yttrium aluminium garnet (YAG) is a synthetic crystalline material of the garnet group.

YAG for a period was used in jewelry as a diamond and other gemstone simulant. Colored variants and their doping elements include: green (chromium), blue (cobalt), red (manganese), yellow (titanium), purple (neodymium), pink, and orange. As faceted gems they are valued (as synthetics) for their clarity, durability, high refractive index and dispersion. The critical angle of YAG is 33 degrees. YAG cuts similar to natural garnet, with polishing being performed with alumina or diamond (50,000 or 100,000) on common polishing laps. YAG has low heat sensitivity.

As a synthetic gemstone YAG has numerous varietal and trade names, as well as a number of misnomers. Synonymous names include: alexite, amamite, circolite, dia-bud, diamite, diamogem, diamonair, diamone, diamonique, diamonite, diamonte, di'yag, geminair, gemonair, kimberly, Linde simulated diamond, nier-gem, regalair, replique, somerset, triamond, YAIG, and yttrium garnet. Production for the gem trade decreased after the introduction of synthetic cubic zirconia; as of 1995 there was little production. Some demand exists as synthetic garnet, and for designs where the very high refractive index of cubic zirconia is not desirable.

Yttrium Aluminium Garnet Properties

Chemical Composition: 
Yttrium Aluminium Oxide - Y3Al15O12
Classification / Type: 
Y.A.G. is a man made material with a garnet internal structure. The term synthetic is not used to refer to this material since it does not have a natural counterpart.
Colors / Varieties: 
Colorless, blue, green, yellow, lilac, pink.
Crystal System / Forms: 
Cubic System
Hardness: 
8.5
Specific Gravity: 
4.55 - 4.60; may vary with dopants used.
Cleavage / Fracture: 
None / Conchoidal fracture
Optic Character: 
Isotropic (S.R.)
Lustre: 
Adamantine to vitreous.
Refractive Index / Birefringence: 
1.833
Pleochroism: 
Nil
Dispersion: 
0.028
Magnification: 
Gas bubbles aligned in fingerprints, twisted droplets, and stringers.
U.V. Fluorescence: 
Varies with dopants used.
Spectrum: 
Varies with dopants used.
Cause of Color: 
  • Green: Chromium
  • Blue: Cobalt
  • Purple: Neodymium
  • Red / Pink: Manganese
Specific Tests: 
Strong see-through effect.
Synthesis: 
Czochralski method.
Simulants (with separation tests): 
G.G.G. (S.G.), Synthetic Cubic Zirconia (S.G., dispersion), Zircon (spectrum, optic character, doubling), Sphene (optic character, doubling, dispersion), Strontium Titanate (dispersion, S.G.), Synthetic Rutile (optic character, dispersion), Diamond (dispersion, inclusions, S.G.), Demantoid (inclusions, spectrum, S.G.), Spessartite Garnet (spectrum, inclusions, S.G.), etc.
Geological Occurrence: 
In a laboratory. No natural counterpart.
Cuts & Uses: 
Facetted cuts, beads, etc.
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One of the first gemstones to be mined, turquoise has long been prized for its intense color, which varies from sky-blue to green, depending on the quantities of iron and copper within it. Turquoise is commonly found in microcrystalline, massive form, usually as encrustations, in veins, or as nodules. It is opaque to semi-translucent, light and very fragile, with conchoidal fracture. Some material is very porous, leading to fading and cracking, so it may be impregnated with wax or resin to maintain its appearance.

Sky blue turquoise from Iran is generally regarded as the most desirable; but in Tibet a greener variety is preferred. Localities in Mexico and United States produce a greener, more porous material that tends to fade more quickly. Other localities include the former USSR, Chile, Australia, Turkistan and Cornwall (England).

Turquoise has been thought to warn the wearer of danger or illness by changing color. It has been imitated by stained howlite, fossil bone or tooth, limestone, chalcedony, glass, and enamel. In 1972, an imitation turquoise was produced in France by Gilson.

Turquoise Properties

Chemical Composition: 
Hydrous copper aluminium phosphate, with traces of Iron. CuAl6(PO4)4(OH)8.5H2O
Colors / Varieties: 
  • Opaque blue, blue - green, greenish - blue, yellowish - green. Green (increasing Fe %)
  • Turquoise matrix: contains parts of the mother rock.
  • Spiderweb turquoise: matrix resembling a spider web pattern.
Crystal System / Forms: 
Triclinic System / Cryptocrystalline aggregates, massive, varying porosity.
Hardness: 
5.5 - 6
Specific Gravity: 
Range: 2.60 - 2.85 (varies with porosity)
Cleavage / Fracture: 
None / Conchoidal fracture with a dull to waxy lustre.
Optic Character: 
Anisotropic, D.R.; Biaxial positive. Aggregate (A.G.G. to Opaque).
Lustre: 
Polished surfaces are waxy to vitreous.
Refractive Index / Birefringence: 
1.610 - 1.650 (Spot R.I. 1.610) / 0.040.
Pleochroism: 
None.
Magnification: 
Matrix background may contain blackish metallic inclusions.
U.V. Fluorescence: 
Greenish yellow to blue in longwave and inert in shortwave.
Spectrum: 
Weak bands at 460nm, line at 432nm
Cause of Color: 
Blue - copper; green - copper and iron.
Treatment (Enhancement): 
  • Colorless impregnation: Use of plastic, paraffin, waxes to seals the pores and improves durability and surface lustre. Surface coating may be used.
  • Colored impregnation (dyeing): Use of color / yellow - brown metallic material to improve color and / or introduce a matrix effect.
Specific Tests: 
  • Because of porosity, should be treated with care. Body oils and perfumes may be absorbed and cause splotches of discoloration, and also a change of color.
  • Dissolves slowly in hydrochloric acid.
Synthesis: 
Gilson synthetic turquoise by the ceramic method.
Simulants (with separation tests): 
  • Synthetic turquoise: regular surface texture with blue spheres in a white background, blue thread like inclusions.
  • Reconstructed turquoise (plastic / resin bonded): Hot point test will give typical odor.
  • Variscite (R.I., structure, spectrum), Chrysocolla (R.I., S.G., texture), Plastic (S.G., structure), Glass (lustre, inclusions), Pectolite (structure, spectrum, birefringence), amazonite (structure, R.I., S.G.), Dyed Blue Howlite (spectrum, structure) etc.
Geological Occurrence: 
In areas of copper deposits, in porphyry and trachyte rocks.
Sources: 
Iran (least porous), U.S.A. (Arizona, New Mexico), Tibet, Mexico, Egypt, Australia, China
Cuts & Uses: 
Cabochon, beads, carvings, tumbled, etc.
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