Anhydrite

Anhydrite is a mineral—anhydrous calcium sulphate, CaSO₄.

Anhydrite
Anhydrite, Chihuahua, Mexico
General
Category	Sulphate mineral
Formula (repeatin unit)	Anhydrous calcium sulphate:CaSO4
Strunz clessification	07.AD.30
Dana clessification	28.3.2.1
Creestal seestem	Orthorhombic – dipyramidal
Space group	Orthorhombic 2/m 2/m 2/m
Unit cell	a = 6.245(1) Å, b = 6.995(2) Å, c = 6.993(2) Å; Z = 4
Identification
Colour	Colourless tae fauch blae or violet gif transparent; white, mauve, rose, fauch broun or gray frae includit impurities
Creestal habit	Rare tabular an prismatic crystals. Uisually occurs as fibrous, parallel veins that break aff intae cleavage fragments. Occurs as grainy, massive, or nodular masses an aw.
Twinnin	Simple or repeatitly on {011} common; contact twins rare on {120}
Cleavage	[010] perfect [100] perfect [001] guid, resultin in pseudocubic fragments
Fractur	Conchoidal
Tenacity	Brickle
Mohs scale haurdness	3.5
Skinkle	Pearly on {010} vitreous tae glittie on {001} vitreous on {100}
Streak	White
Diaphaneity	Skyre tae leamin
Speceefic gravity	2.97
Optical properties	Biaxial (+)
Refractive index	nα = 1.567–1.574 nβ = 1.574–1.579 nγ = 1.609–1.618
Birefringence	δ = 0.042–0.044
Pleochroism	For violet varieties X = colourless tae fauch yellae or rose Y = fauch violet or rose Z = violet.
2V angle	56–84°
Fusibility	2
Ither chairacteristics	Some specimens fluoresce; mony mair fluoresce efter heatin
References	[1][2][3][4]