Zoisite Gemstones by Size
This table shows distribution of Zoisite gemstone sizes that are listed on this site. This can give a good indication as to the general availability of this gemstone in different sizes.
0.20ct to 156.84ct156.84ct to 313.49ct313.49ct to 470.13ct470.13ct to 626.77ct626.77ct to 783.42ct783.42ct to 940.06ct940.06ct to 1,096.70ct1,096.70ct to 1,253.34ct1,253.34ct to 1,409.99ct1,409.99ct to 1,566.63ct
| General Information |
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| Varieties/Types: | Anyolite - Green Zoicite rock with black hornblende inclusions and large ruby crystals. Tanzanite - A variety of Zoisite with a blue to blue-violet colour. Thulite - A pink variety of Zoisite forming opaque masses. |
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| Chemical Formula | Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) More from other references |
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| Zoisite Treatments |
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The mineral zoisite, Ca2Al3Si3O12OH, also occurs in a gem form called tanzanite, discovered only in 1967 (Hurlbut, 1969). Although a few, deep violet-blue dichroic crystals have been found, the majority of this material occurs with a brownish color having a strong violet-red/deep blue/yellow-green trichroism. Heating for about 2 h to 370°C converts the yellow-green component into a deep blue, leaving only a violet-red/deep blue dichroism and the desired color closely resembles sapphire. Some material is said to require a temperature over 600°C. The color is stable to 900°C, but above this temperature water is lost and a dirty yellow results. The causes of the color and color change have not yet been established with certainty; Gubelin and Weibel have summarized this and the gemology (Gubelin and Weibel, 1976) - Nassau (1984)
Heat-treatment of brownish-greenish-bluish crystals produces Tanzanite color - Blue Chart Gem Identification, Herve Nicolas Lazzarelli, 2010, p 3 |
| Physical Properties of Zoisite |
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| Mohs Hardness | 6 to 7Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references |
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| Specific Gravity | 3.20 to 3.50Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references |
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| Cleavage Quality | PerfectUlrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) More from other references |
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| Fracture | ConchoidalArthur Thomas, Gemstones (2009) |
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| Optical Properties of Zoisite |
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| Refractive Index | 1.685 to 1.707Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references |
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| Optical Character | Biaxial/+Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references |
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| Birefringence | 0.006 to 0.013Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references |
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| Pleochroism | StrongArthur Thomas, Gemstones (2009) |
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| Dispersion | 0.0196Arthur Thomas, Gemstones (2009) |
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| Chatoyancy | RareHerve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) |
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| Colour |
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| Colour (General) | Green, brown, red-violet, bluish-greenUlrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) More from other references |
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| Causes of Colour | Blue, (tanzanite - heat treated), V4+ in octahedral coordination; with V3+ in octahedral coordination. Brown-violet, V3+ in octahedral coordination (treatment turns blue, tanzanite). Green, Cr3+ in octahedral coordination. Pink (thulite), Mn3+ in presumably octahedral coordinationW. William Hanneman, Pragmatic Spectroscopy For Gemologists (2011) |
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| Transparency | Transparent,Translucent,OpaqueUlrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) More from other references |
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| Lustre | VitreousArthur Thomas, Gemstones (2009) |
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| Crystallography of Zoisite |
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| Crystal System | OrthorhombicHerve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references |
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| Habit | PrismaticMichael O’Donoghue, Gems, Sixth Edition (2006) More from other references |
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| Geological Environment |
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| Where found: | Occurs in medium-grade regionally metamorphosed crystalline schists formed from igneous, sedimentary or metamorphic rocks relatively high in calcium.Michael O’Donoghue, Gems, Sixth Edition (2006) |
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| Inclusions in Zoisite |
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"Fingerprint", graphite (black), hematite (hexagonal) - Blue Chart Gem Identification, Herve Nicolas Lazzarelli, 2010, p 3
Healing cracks, growth tubes, graphite - Gemmological Tables, Ulrich Henn and Claudio C. Milisenda, 2004, p 20 |
| Further Information |
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| Mineral information: | Zoisite information at mindat.org |
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| Significant Gem Localities |
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