Variscite

Variscite
General
Category Phosphate minerals
Formula
(repeating unit)		 AlPO4·2H2O
Strunz classification 08.CD.10
Identification
Color Green, blue green, yellow green and rarely red
Crystal habit Encrustations and reniform masses
Crystal system Orthorhombic - dipyramidal
Cleavage [010] perfect
Fracture Conchoidal to splintery
Mohs scale hardness 4.5
Luster Vitreous to waxy
Streak White
Diaphaneity Transparent to translucent
Specific gravity 2.57 to 2.61
Optical properties Biaxial (-)
Refractive index nα = 1.563 nβ = 1.588 nγ = 1.594
Birefringence δ = 0.031
References [1][2][3]

Variscite is a hydrated aluminium phosphate mineral (AlPO4·2H2O). It is a relatively rare phosphate mineral. It is sometimes confused with turquoise; however, variscite is usually greener in color.

Variscite is a secondary mineral formed by direct deposition from phosphate-bearing water that has reacted with aluminium-rich rocks in a near-surface environment.[4] It occurs as fine-grained masses in nodules, cavity fillings, and crusts. Variscite often contains white veins of the calcium aluminium phosphate mineral crandallite.

Variscite is sometimes used as a semi-precious stone, and is popular for carvings and ornamental use. It was first described in 1837 and named for the locality of Variscia, the historical name of the Vogtland, in Germany. At one time, variscite was called Utahlite. At times, materials which may be turquoise or may be variscite have been marketed as "variquoise". Appreciation of the color ranges typically found in variscite have made it a popular gem in recent years.[5]

Variscite from Nevada typically contains black spiderwebbing in the matrix and is often confused with green turquoise. Most of the Nevada variscite recovered in recent decades has come from mines located in Lander County.[6]

Notable localities are Lucin, Utah and Fairfield, Utah in the United States. It is also found in Germany, Australia, Poland, Spain[7] and Brazil.

See also

References

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  1. ↑ http://rruff.geo.arizona.edu/doclib/hom/variscite.pdf Mineral Data Publishing - PDF
  2. ↑ http://www.mindat.org/min-4156.html Mindat
  3. ↑ http://webmineral.com/data/Variscite.shtml Webmineral data
  4. ↑ Roncal-Herrero, T., Rodriguez-Blanco, J.D., Benning, L.G., Oelkers, E.H. (2009) Precipitation of Iron and Aluminum Phosphates Directly from Aqueous Solution as a Function of Temperature from 50 to 200°C. Crystal Growth & Design, 9, 5197-5205. doi: 10.1021/cg900654m.
  5. ↑ Minerals of Nevada - Nevada Bureau of Mines Special Pub. 31 University of Nevada Press, 2004 Pages 78-81
  6. ↑ Gemstones of North America Volume III by John Sinkankas - Geoscience Press 1997
  7. ↑ http://www.patrimonigava.cat/esp/imgpcn/m.asp