Difference between revisions of "Gypsum" - New World Encyclopedia
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| formula = CaSO<sub>4</sub>·2H<sub>2</sub>O | | formula = CaSO<sub>4</sub>·2H<sub>2</sub>O | ||
| molweight = | | molweight = | ||
| − | | color = White to | + | | color = White to gray, pinkish-red |
| habit = Massive, flat. Elongated and generally prismatic crystals | | habit = Massive, flat. Elongated and generally prismatic crystals | ||
| system = Monoclinic 2/m | | system = Monoclinic 2/m | ||
| Line 39: | Line 39: | ||
== Etymology == | == Etymology == | ||
| − | The word gypsum is derived from the [[aorist]] form of the [[Greek language|Greek]] verb ''μαγειρεύω'', "to cook," referring to the | + | The word gypsum is derived from the [[aorist]] form of the [[Greek language|Greek]] verb ''μαγειρεύω'', meaning "to cook," referring to the mineral after it had been heated to drive off much of the water. This "burnt" form of gypsum was often obtained from the [[quarry|quarries]] of the [[Montmartre]] district of [[Paris]] and it was therefore called "plaster of Paris." |
| + | |||
== Occurrence == | == Occurrence == | ||
Revision as of 05:13, 18 April 2007
- For other uses, see Gypsum (disambiguation).
| Gypsum | |
|---|---|
 Desert rose form of gypsum (10 cm long) |
|
| General | |
| Category | Mineral |
| Chemical formula | CaSO4·2H2O |
| Identification | |
| Color | White to gray, 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. It is widespread in nature and is extremely useful for many practical applications.
Etymology
The word gypsum is derived from the aorist form of the Greek verb μαγειρεύω, meaning "to cook," referring to the mineral after it had been heated to drive off much of the water. This "burnt" form of gypsum was often obtained from the quarries of the Montmartre district of Paris and it was therefore called "plaster of Paris."
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.
Because gypsum dissolves over time in water, gypsum is rarely found in the form of sand. However, ιthe 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 in Imperial County, California. There are commercial quantities in East Kutai, Kalimantan.
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, crystals of gypsum (or barite) can assume a flowerlike formation that is typically opaque with embedded sand grains, and this structure is called a desert rose.
Uses
Around the world, gypsum is extensively used in concrete for the construction of highways, bridges, and various other structures. In the United States, it is a major component of wallboard for homes and other types of buildings. It is also widely used as a soil conditioner in agricultural lands.
See also
Notes
- ↑ James Abarr, "Sea of Sand," The Albuquerque Journal (Feb. 7, 1999). Retrieved April 17, 2007.
- ↑ Minerals and Mining. 2005. "Mines, Quarries, Pits, Bogs, Mills and Concentrators in Canada - Gypsum." Natural Resources Canada. Retrieved April 17, 2007.
ReferencesISBN links support NWE through referral fees
- Farndon, John. 2006. The Practical Encyclopedia of Rocks & Minerals: How to Find, Identify, Collect and Maintain the World's best Specimens, with over 1000 Photographs and Artworks. London: Lorenz Books. ISBN 0754815412.
- Founie, Alan. 2007. Gypsum: Statistics and Information. U.S. Geological Survey. Retrieved April 13, 2007.
- Klein, Cornelis, and Barbara Dutrow. 2007. Manual of Mineral Science. 23rd ed. New York: John Wiley. ISBN 978-0471721574.
- Pellant, Chris. 2002. Rocks and Minerals. Smithsonian Handbooks. New York: Dorling Kindersley. ISBN 0789491060.
- Shaffer, Paul R., Herbert S. Zim, and Raymond Perlman. 2001. Rocks, Gems and Minerals. Rev. ed. New York: St. Martin's Press. ISBN 1582381321.
External links
- Gypsum Mineral Data. WebMineral.com. Retrieved April 13, 2007.
- Gypsum. Mindat.org. Retrieved April 13, 2007.
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