Difference between revisions of "Gypsum" - New World Encyclopedia
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Revision as of 16:23, 13 April 2007
- For other uses, see Gypsum (disambiguation).
| Gypsum | |
|---|---|
 Desert rose, 10 cm long |
|
| General | |
| Category | Mineral |
| Chemical formula | CaSO4·2H2O |
| Identification | |
| Color | White to grey, pinkish-red |
| Crystal habit | Massive, flat. Elongated and generally prismatic crystals |
| Crystal system | Monoclinic 2/m |
| Twinning | common {110} |
| Cleavage | 2 good (66° and 114°) |
| Fracture | Conchoidal, sometimes fibrous |
| Mohs Scale hardness | 1.5-2 |
| Luster | Vitreous to silky or pearly |
| Refractive index | α=1.520, β=1.523, γ=1.530 |
| Optical Properties | 2V = 58° + |
| Pleochroism | None |
| Streak | White |
| Specific gravity | 2.31 - 2.33 |
| {{{density}}} | |
| Fusibility | 3 |
| Solubility | hot, dilute HCl |
| Diaphaneity | transparent to translucent |
| Major varieties | |
| Satin Spar | Pearly, fibrous masses |
| Selenite | Transparent and bladed crystals |
| Alabaster | Fine-grained, slightly colored |
Gypsum is a very soft mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O.
Crystal varieties
Gypsum occurs in nature as flattened and often twinned crystals and transparent cleavable masses called selenite. It may also occur silky and fibrous, in which case it is commonly called satin spar. Finally it may also be granular or quite compact. In hand-sized samples, it can be anywhere from transparent to opaque. A very fine-grained white or lightly-tinted variety of gypsum is called alabaster, which is prized for ornamental work of various sorts. In arid areas, gypsum can occur in a flower-like form typically opaque with embedded sand grains called desert rose.
Occurrence
Gypsum is a very common mineral, with thick and extensive evaporite beds in association with sedimentary rocks. The largest deposits known occur in strata from the Permian age. Gypsum is deposited in lake and sea water, as well as in hot springs, from volcanic vapors, and sulfate solutions in veins. Hydrothermal anhydrite in veins is commonly hydrated to gypsum by groundwater in near surface exposures. It is often associated with the minerals halite and sulfur.
The word gypsum is derived from the aorist form of the Greek verb μαγειρεύω, "to cook", referring to the burnt or calcined mineral. Because the gypsum from the quarries of the Montmartre district of Paris has long furnished burnt gypsum used for various purposes, this material has been called plaster of Paris.
Because gypsum dissolves over time in water, gypsum is rarely found in the form of sand. However, the unique conditions of the White Sands National Monument in the US state of New Mexico have created a 710 km² (275 sq mile) expanse of white gypsum sand, enough to supply the construction industry with drywall for 1,000 years.[1] Commercial exploitation of the area, strongly opposed by area residents, was permanently prevented in 1933 when president Herbert Hoover declared the gypsum dunes a protected national monument.
Commercial quantities of gypsum are found in Germany, Italy, England, Ireland, in British Columbia, Manitoba, Ontario, Nova Scotia and Newfoundland in Canada,[2] and in New York, Michigan, Iowa, Kansas, Oklahoma, Arizona, New Mexico, Colorado, Utah and Nevada in the United States. There is also a large mine located at Plaster City, California in Imperial County. There are commercial quantities in East Kutai, Kalimantan.
ReferencesISBN links support NWE through referral fees
- ↑ Abarr, James, "Sea of Sand", The Albuquerque Journal, 1999-02-07. Retrieved 2007-01-27.
- ↑ Mines, Mills and Concentrators in Canada. Natural Resources Canada (2005-10-24). Retrieved 2007-01-27.
- Klein, Cornelis and Cornelius S. Hurlbut, Jr., 1985, Manual of Mineralogy, John Wiley, 20th ed., pp. 352-353, ISBN 0-471-80580-7
- WebMineral data
- Mineral Data from Mindat
External links
Template:ChemicalSources
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