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.

Anhydrite Gemstones by Colour

This table shows the variety of hues this gemstone can be found in. Click on a photo for more information.
 

Anhydrite Gemstones by Size

This table shows distribution of Anhydrite 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.
Contributed photos
Lightest:2.30 cts
Heaviest:3.89 cts
Average:3.10 cts
Total photos:2
Do you have a larger Anhydrite? Why not upload a photo?
2.30ct to 2.46ct2.46ct to 2.62ct2.62ct to 2.78ct2.78ct to 2.94ct2.94ct to 3.10ct3.10ct to 3.25ct3.25ct to 3.41ct3.41ct to 3.57ct3.57ct to 3.73ct3.73ct to 3.89ct
General Information
Varieties/Types:
Chemical Formula
CaSO
 
4
Michael O’Donoghue, Gems, Sixth edition (2006)
More from other references
Photos of natural/un-cut material from mindat.org
Physical Properties of Anhydrite
Mohs Hardness3.5
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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Specific Gravity2.90 to 2.98
Walter Schumann, Gemstones of the world (2001)
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Cleavage QualityPerfect
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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FractureUneven
Arthur Thomas, Gemstones (2009)
Optical Properties of Anhydrite
Refractive Index1.570 to 1.614
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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Optical CharacterBiaxial/+
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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Birefringence0.044
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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PleochroismWeak
Arthur Thomas, Gemstones (2009)
Dispersion0.013
Arthur Thomas, Gemstones (2009)
Colour
Colour (General)Colourless to light pink, pale blue to violet.
Michael O’Donoghue, Gems, Sixth edition (2006)
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TransparencyTransparent,Translucent
Michael O’Donoghue, Gems, Sixth edition (2006)
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LustreVitreous
Arthur Thomas, Gemstones (2009)
Fluorescence & other light emissions
Fluorescence (Long-Wave UV)Some German anhydrite may show a red fluorescence under LWUV.
Michael O’Donoghue, Gems, Sixth edition (2006)
Crystallography of Anhydrite
Crystal SystemOrthorhombic
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
More from other references
HabitTabular or equant crystals
Michael O’Donoghue, Gems, Sixth edition (2006)
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Geological Environment
Where found:Is usually formed by the dehydration of gypsum
Michael O’Donoghue, Gems, Sixth edition (2006)
Further Information
Mineral information:Anhydrite information at mindat.org
Significant Gem Localities
Canada
 
  • Ontario
    • Hastings Co.
      • Faraday Township
Gems, Sixth Edition, Michael O’Donoghue, 2006, p. 382
Mexico
 
  • Chihuahua
    • Saucillo Municipality
      • Naica
Gems, Sixth Edition, Michael O’Donoghue, 2006, p. 382
Peru
 
  • Arequipa
    • Huanquarque
[var: Angelite]
Switzerland
 
  • Valais
    • Brig
      • Simplon pass area
Gems, Sixth Edition, Michael O’Donoghue, 2006, p. 382
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