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Gypsum is a very saft sulfate meeneral componed o calcium sulfate dihydrate, wi the chemical formula CaSO4·2H2O.[3] It can be uised as a fertilizer, is the main constituent in mony furms o plaister an is widely mined. A very fine-grained white or lichtly tinted variety o gypsum, cried alabast, haes been uised for sculpture bi mony culturs includin Auncient Egyp, Mesopotamie an the Nottingham alabasts o medieval Ingland. It is the definition o a hairdness o 2 on the Mohs scale o meeneral hardness. It furms as an evaporite meeneral an as a hydration product o anhydrite.

Fibrous gypsum selenite shawin its translucent property.
Category Sulfate meenerals
(repeatin unit)
Strunz clessification 07.CD.40
Creestal seestem Monoclinic 2/m – Prismatic
Space group Monoclinic 2/m
Unit cell a = 5.679(5) Å, b = 15.202(14) Å, c = 6.522(6) Å; β = 118.43°; Z=4
Colour Colourless tae white; mey be yellae, tan, blue, pink, broun, reiddish brown or gray due tae impurities
Creestal habit Massive, flat. Elangatit an generally prismatic crystals
Twinnin Very common on {110}
Cleavage Perfect on {010}, distinct on {100}
Fractur Conchoidal on {100}, splintery parallel tae [001]
Tenacity Flexible, inelastic.
Mohs scale haurdness 1.5–2 (definin meeneral for 2)
Skinkle Vitreous tae silky, pearly, or waxy
Streak White
Diaphaneity Transparent tae translucent
Speceefic gravity 2.31–2.33
Optical properties Biaxial (+)
Refractive index nα = 1.519–1.521
nβ = 1.522–1.523
nγ = 1.529–1.530
Birefringence δ = 0.010
Pleochroism None
2V angle 58°
Fusibility 5
Solubility Het, dilute HCl
References [1][2][3]
Major varieties
Satin spar Pearly, fibrous masses
Selenite Transparent and bladed crystals
Alabast Fine-grained, slightly colored


  1. Gypsum in Handbook of Mineralogy
  2. Gypsum at Mindat
  3. 3.0 3.1 Cornelis Klein and Cornelius S. Hurlbut, Jr., 1985, Manual of Mineralogy, John Wiley, 20th ed., pp. 352–353, ISBN 0-471-80580-7