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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

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.

References[eedit | eedit soorce]

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