Anhydrite
Anhydrite was named by A. G. Werner in 1804, from Greek "an" - without and "hydor" - water, because of the absence of water of crystallization, in contrast with the presence of water in gypsum.
When exposed to water, anhydrite transforms to
gypsum by the absorption of water. This transformation is reversible,
gypsum forms anhydrite by heating to ~200°C under normal atmospheric conditions.
Fine specimens are very rare. Small crystals and pieces of clean facet-grade rough are found in salt mines. Anhydrite is very rarely faceted or cut as cabochons.
General Information |
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Varieties/Types: | |
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Chemical Formula | Michael O’Donoghue, Gems, Sixth edition (2006) More from other references |
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Photos of natural/un-cut material from mindat.org |
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Physical Properties of Anhydrite |
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Mohs Hardness | 3.5Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) More from other references |
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Specific Gravity | 2.90 to 2.98Walter Schumann, Gemstones of the world (2001) 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 | UnevenArthur Thomas, Gemstones (2009) |
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Optical Properties of Anhydrite |
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Refractive Index | 1.570 to 1.614Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) More from other references |
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Optical Character | Biaxial/+Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) More from other references |
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Birefringence | 0.044Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) More from other references |
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Pleochroism | WeakArthur Thomas, Gemstones (2009) |
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Dispersion | 0.013Arthur Thomas, Gemstones (2009) |
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Colour |
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Colour (General) | Colourless to light pink, pale blue to violet.Michael O’Donoghue, Gems, Sixth edition (2006) More from other references |
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Transparency | Transparent,TranslucentMichael O’Donoghue, Gems, Sixth edition (2006) More from other references |
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Lustre | VitreousArthur Thomas, Gemstones (2009) |
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Fluorescence & other light emissions |
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Fluorescence (Long-Wave UV) | Some German anhydrite may show a red fluorescence under LWUV.Michael O’Donoghue, Gems, Sixth edition (2006) |
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Crystallography of Anhydrite |
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Crystal System | OrthorhombicUlrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) More from other references |
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Habit | Tabular or equant crystalsMichael O’Donoghue, Gems, Sixth edition (2006) More from other references |
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Geological Environment |
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Where found: | Is usually formed by the dehydration of gypsumMichael O’Donoghue, Gems, Sixth edition (2006) |
Further Information |
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Mineral information: | Anhydrite information at mindat.org |
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Significant Gem Localities |
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| Canada | |
| Gems, Sixth Edition, Michael O’Donoghue, 2006, p. 382 | | Mexico | |
| Gems, Sixth Edition, Michael O’Donoghue, 2006, p. 382 | | Peru | |
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| [var: Angelite] | | Switzerland | |
| Gems, Sixth Edition, Michael O’Donoghue, 2006, p. 382 |
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