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Variscite



Variscite

General
Categorymineral
Chemical formulaAlPO4·2H2O
Identification
ColorGreen, blue green, yellow green and rarely red
Crystal habitEncrustations and reniform masses
Crystal systemOrthorhombic - Dipyramidal
Cleavage010 perfect
FractureConchoidal to splintery
Mohs Scale hardness4.5
LusterVitreous to waxy
Refractive indexnα = 1.563 nβ = 1.588 nγ = 1.594
Optical PropertiesBiaxial (-)
StreakWhite
Specific gravity2.57 to 2.61

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

Additional recommended knowledge

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. 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 type locality of Variscia, the historical name of 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[1].

Two of the major mines in Utah are the Lucin mine in northern Utah and the Clay Canyon mine 40 minutes southwest of Salt Lake City. Both mines are practically mined out and inactive. Clay Canyon variscite fetches a high dollar and is prized by collectors and jewelry makers for the 10 other kinds of minerals that are found in the material, including wardite and crandelite, that make for very unusual patterns. The US Postal Service put out a stamp with a sample piece of Clay Canyon variscite as a picture on the stamp. Lucin variscite is notable for deep emerald to minty greens and a grey chert matrix.

Variscite from Nevada typically contains black spiderwebbing in the matrix and is often confused with green turquoise. Nevada variscite mines tend to be smaller "one-man" mines. While little Utah Variscite has been produced in recent decades, Nevada produced some significant amounts of carving and gem grade materials since the 1980s. Most of the Nevada variscite recovered in recent decades has come from mines located in Lander County.[2] Productive mines in Lander County include the Damali, Apache Canyon, McGuinness, and several mines in the Ackerman Canyon area. Several mines near Candelaria in Esmerelda County have also been productive, in fact a large strike of Variscite was made at Candelaria in 2005.

A notable locality is Fairfield, Utah in the United States. It is also found in Germany, Australia, Poland and Brazil. 


References

  1. ^ Minerals of Nevada - Nevada Bureau of Mines Special Pub. 31 University of Nevada Press, 2004 Pages 78-81
  2. ^ Gemstones of North America Volume III by John Sinkankas - Geoscience Press 1997
  • Webmineral data
  • Mindat
  • Mineral Data Publishing - PDF

See also

 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Variscite". A list of authors is available in Wikipedia.
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