Gypsum is a very saft sulfate mineral 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 mineral hardness. It furms as an evaporite mineral an as a hydration product o anhydrite.

Fibrous gypsum selenite shawin its translucent property.
CategorySulfate minerals
(repeatin unit)
Strunz clessification07.CD.40
Creestal seestemMonoclinic 2/m – Prismatic
Space groupMonoclinic 2/m
Unit cella = 5.679(5) Å, b = 15.202(14) Å, c = 6.522(6) Å; β = 118.43°; Z=4
ColourColourless tae white; mey be yellae, tan, blue, pink, broun, reiddish brown or gray due tae impurities
Creestal habitMassive, flat. Elangatit an generally prismatic crystals
TwinninVery common on {110}
CleavagePerfect on {010}, distinct on {100}
FracturConchoidal on {100}, splintery parallel tae [001]
TenacityFlexible, inelastic.
Mohs scale haurdness1.5–2 (definin mineral for 2)
SkinkleVitreous tae silky, pearly, or waxy
DiaphaneityTransparent tae translucent
Speceefic gravity2.31–2.33
Optical propertiesBiaxial (+)
Refractive indexnα = 1.519–1.521
nβ = 1.522–1.523
nγ = 1.529–1.530
Birefringenceδ = 0.010
2V angle58°
SolubilityHet, dilute HCl
Major varieties
Satin sparPearly, fibrous masses
SeleniteTransparent and bladed crystals
AlabastFine-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