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{{Infobox mineral
name = Gypsum
category = Sulfate mineral
boxwidth =
boxbgcolor =
image = desert-rose-big.jpg
caption = Desert rose, 10 cm long
formula = Calcium sulfate CaSO4·2H2O
molweight =
color = Colorless to white; with impurities may be yellow, tan, blue, pink, brown, reddish brown or gray
habit = Massive, flat. Elongated and generally prismatic crystals
system = Monoclinic 2/m - Prismatic
twinning = Very common on {110}
cleavage = Perfect on {010}, distinct on {100}
fracture = Conchoidal on {100}, splintery parallel to [001]
mohs = 1.5-2
luster = Vitreous to silky, pearly, or waxy
refractive = nα = 1.519 - 1.521 nβ = 1.522 - 1.523 nγ = 1.529 - 1.530
opticalprop = 2V = 58° Biaxial (+)
birefringence = δ = 0.010
pleochroism = None
streak = White
gravity = 2.31 - 2.33
melt =
fusibility = 5
diagnostic =
solubility = hot, dilute HCl
diaphaneity = transparent to translucent
other =
references =
var1text = Pearly, fibrous masses
var2 = Selenite | var2text = Transparent and bladed crystals
var3 = Alabaster | var3text = 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 in a silky, fibrous form, 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. Up to the size of 11m long, gypsum forms some of the largest crystals found in nature, in the form of selenite.

Occurrence

Gypsum var. selenite from Andamooka Ranges - Lake Torrens area, South Australia
Gypsum is a common mineral, with thick and extensive evaporite beds in association with sedimentary rocks. Deposits are known to occur in strata from as early as 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 Greek word γύψος, "chalk" or "plaster". Because the gypsum from the quarries of the Montmartremarker district of Parismarker has long furnished burnt gypsum used for various purposes, this material has been called plaster of Paris. It is also used in foot creams, shampoos and many other hair products. It is water-soluble.

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 Monumentmarker in the US state of New Mexicomarker have created a 710 km² (275 square mile) expanse of white gypsum sand, enough to supply the construction industry with drywall for 1,000 years. 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 the cities of Araripinamarker and Grajaúmarker, Brazilmarker, Pakistanmarker, Jamaicamarker, Iranmarker, Thailandmarker, Spainmarker (the main producer in Europe), Germanymarker, Italymarker, Englandmarker, Irelandmarker, in British Columbiamarker, Manitobamarker, Ontariomarker, Nova Scotiamarker and Newfoundlandmarker in Canadamarker, and in New Yorkmarker, Michiganmarker, Indianamarker,Texasmarker(in the Palo Duro Canyonmarker),Iowamarker, Kansasmarker, Oklahomamarker, Arizonamarker, New Mexicomarker, Coloradomarker, Utahmarker and Nevadamarker in the United Statesmarker. There is also a large open pit quarry located at Plaster Citymarker, California in Imperial County, and in East Kutai, Kalimantan.

Crystals of gypsum up to 11 meters long have been found in the caves of the Naica Mine of Chihuahuamarker, Mexicomarker. The crystals thrived in the cave's extremely rare and stable natural environment. Temperatures stayed at 58 °C, and the cave was filled with mineral-rich water that drove the crystals' growth. The largest of those crystals weighs 55 tons and is around 500,000 years old.

Synthetic gypsum is recovered via flue gas desulfurization at some coal-fired electric power plants. It can be used interchangeably with natural gypsum in some applications.

Orbital pictures from the Mars Reconnaissance Orbiter indicate the existence of gypsum dunes in the northern polar region of Mars.

Uses of Gypsum

Gypsum is used in a wide variety of applications:
  • Gypsum Board primarily used as a finish for walls and ceilings; known in construction slang as Drywall
  • Plaster ingredient.
  • Fertilizer and soil conditioner. In the late eighteenth and early nineteenth century, Nova Scotia gypsum, often referred to as plaister, was a highly sought fertilizer for wheat fields in the United States. It is also used in ameliorating sodic soils.
  • A Binder in Fast-Dry tennis court clay.
  • Plaster of Paris (surgical splints; casting moulds; modeling).
  • A wood substitute in the ancient world; for example, when wood became scarce due to deforestation on Bronze Age Cretemarker, gypsum was employed in building construction at locations where wood was previously used.
  • A tofu (soy bean curd) coagulant, making it ultimately a major source of dietary calcium, especially in Asian cultures which traditionally use few dairy products.
  • Adding hardness to water used for homebrewing.
  • Blackboard chalk.
  • A component of Portland cement used to prevent flash setting of concrete.
  • Soil/water potential monitoring (soil moisture tension)
  • Has a common use as an ingredient in making mead.
  • A medicinal agent in traditional Chinese medicine called Shi Gao.


References

  1. http://rruff.geo.arizona.edu/doclib/hom/gypsum.pdf Handbook of Mineralogy
  2. http://www.mindat.org/min-1784.html Mindat
  3. Cornelis Klein and Cornelius S. Hurlbut, Jr., 1985, Manual of Mineralogy, John Wiley, 20th ed., pp. 352-353, ISBN 0-471-80580-7
  4. Barry F. Beck, Felicity M. Pearson, P.E. LaMoreaux & Associates, National Groundwater Association (U.S.), Karst Geohazards: Engineering and Environmental Problems in Karst Terrane, 1995, Taylor & Francis, 581 pages ISBN 9054105356
  5. [1] Electric Caverns - picture from Peñoles Mine - article also includes a link to a picture of a spectacular gypsum flower at Lechuguilla Cave
  6. http://hirise.lpl.arizona.edu/nea.php
  7. * Complimentary list of MasterFormat 2004 Edition Numbers and Titles (large PDF document)
  8. Oster and Frenkel. 1980. The Chemistry of the Reclamation of Sodic Soils with Gypsum and Lime. SSSAJ. 44:41-45
  9. C. Michael Hogan, Knossos fieldnotes, Modern Antiquarian (2007)


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