Variscite
| Variscite | |
|---|---|
 | |
| General | |
| Category | Phosphate minerals |
| Formula (repeating unit) | AlPO4·2H2O |
| Strunz classification | 8.CD.10 |
| Crystal system | Orthorhombic |
| Crystal class |
Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) |
| Space group | Pbca |
| Identification | |
| Color | Green, blue green, yellow green and rarely red |
| Crystal habit | Encrustations and reniform masses |
| 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.
Cut slab of Variscite at the Smithsonian. Specimen is roughly 0.5 m wide.
Variscite filling the cracks in siltstone. The sample is from Queensland, Australia. The width of the view is 11 cm (4.3 in).
Gem quality variscite, Nevada.
See also
References
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Wikimedia Commons has media related to Variscite. |
- ↑ http://rruff.geo.arizona.edu/doclib/hom/variscite.pdf Mineral Data Publishing - PDF
- ↑ http://www.mindat.org/min-4156.html Mindat
- ↑ http://webmineral.com/data/Variscite.shtml Webmineral data
- ↑ Roncal-Herrero, T.; Rodríguez-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 (12): 5197–5205. doi:10.1021/cg900654m.
- ↑ Minerals of Nevada - Nevada Bureau of Mines Special Pub. 31 University of Nevada Press, 2004 Pages 78-81
- ↑ Gemstones of North America Volume III by John Sinkankas - Geoscience Press 1997
- ↑ http://www.patrimonigava.cat/lahistoriajaciment