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Fibrous gypsum selenite shawin its translucent property.
Category Sulfate minerals
(repeating unit)
Strunz classification 07.CD.40
Crystal symmetry 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
Color Colourless tae white; mey be yellae, tan, blue, pink, broun, reiddish brown or gray due tae impurities
Crystal habit Massive, flat. Elangatit an generally prismatic crystals
Crystal seestem Monoclinic 2/m – Prismatic
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 hairdness 1.5–2 (definin mineral for 2)
Luster Vitreous tae silky, pearly, or waxy
Streak White
Diaphaneity Transparent tae translucent
Specific 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

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. 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