Gypsum

Gypsum is a very saft sulfate mineral componed o calcium sulfate dihydrate, wi the chemical formula CaSO₄·2H₂O. 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.

Gypsum
Fibrous gypsum selenite shawin its translucent property.
General
Category	Sulfate minerals
Formula (repeatin unit)	CaSO4·2H2O
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
Identification
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 mineral 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
Major varieties
Satin spar	Pearly, fibrous masses
Selenite	Transparent and bladed crystals
Alabast	Fine-grained, slightly colored