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Gypsum

2007 Schools Wikipedia Selection. Related subjects: Mineralogy

                                      Gypsum
                             Desert rose, 10 cm long
                                     General
   Category            Mineral
   Chemical formula    CaSO[4]·2H[2]O
                                  Identification
   Colour              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
   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 CaSO[4]·2H[2]O.

Crystal varieties

   Gypsum from New South Wales, Australia
   Gypsum from New South Wales, Australia

   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. The most visually striking variety, however, is the giant
   crystals from Naica Mine. Up to the size of 11m long, these
   megacrystals are among the largest crystals found in nature. A recent
   publication shows that these crystals are grown under very constant
   temperature such that large crystals can grow slowly but steadily
   without excessive nucleation.

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.
   Fibrous Gypsum from Brazil
   Fibrous Gypsum from Brazil

   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. It is also used in foot
   creams, shampoos and many other hair products.

   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. 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, 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.

Uses of Gypsum

   1. Drywall

   2. Plaster ingredient.

   3. Fertilizer and soil conditioner.

   4. Plaster of Paris (surgical splints; casting moulds; modeling).

   5. A tofu (soy bean curd) coagulant, making it ultimately a major
   source of dietary calcium, especially in Asian cultures which
   traditionally use very little dairy products.
   Retrieved from " http://en.wikipedia.org/wiki/Gypsum"
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