Mineral Type - Anhydrite / Angellite

Name

Named in 1804 by Abraham Gottlob Werner from the Greek άνυδρος ("anhydros") meaning "without water", in allusion to the lack of water in its composition, in contrast to gypsum, which contains water.

Physical Properties

Lustre: Vitreous, Greasy, Pearly
Transparency: Transparent, Translucent
Colour: Colourless, bluish, blue-grey, violet, burgundy-red, white, rose-pink, brownish, reddish, grey, dark grey; colourless in transmitted light
Streak: White, off-white, greyish
Hardness: 3 - 3½ on Mohs scale
Tenacity: Brittle
Cleavage: Perfect. On {010} perfect; on {100} nearly perfect; on {001} good to imperfect
Fracture: Irregular/Uneven, Splintery
Density: 2.98(1) g/cm3 (Measured) 2.95 g/cm3 (Calculated)

Chemical Properties

Formula: CaSO4
Elements listed: Ca, O, S
Common Impurities: Sr,Ba,H2O

Crystallography

Crystal System: Orthorhombic
Class (H–M): mmm (2/m 2/m 2/m) - Dipyramidal
Morphology: Crystals equant, or nearly so, with large pinacoidal faces. Also thick tabular on {010}, {100}, or {001}; elongated [100] or [001]. Massive. Fine granular to scaly; fibrous (either parallel, radiated or plumose) and frequently curved. Contorted concretionary forms (bowel stone).
Twinning: 1.) On {011} as contact twins and polysynthetic lamellae (may be produced by heating or pressure); 2.) On {120} as contact twins, rare.

Synonyms

Anhydrous Gypsum, Anhydrous Sulfate of Lime, Cube Spar, Karstenite, Muriacite, and Siliceous Anhydrous Gypsum

Varieties

Angelite, Bowel Stone, and Vulpunite