Anhydrite

Formula:  CaSO₄

Origin of name:  From Greek for without water

Crystal system:  Orthorhombic

Crystal class:  2/m 2/m 2/m

Twinning:  On {011}; rare on {120}

Unit cell:   a = 6.238 Å, b = 6.991 Å, c = 6.996 Å

Colour:  Colourless, white, gray, bluish, violet, pink, red, brown

Diaphaneity: Transparent to translucent

Luster:  Vitreous to greasy to pearly

Habit:  Crystals equant, thick tabular or prismatic, rare; usually massive, granular

Hardness:  3.5

Specific gravity:  2.98

Cleavage:  3; {010} perfect, {100} nearly perfect, {001} good to imperfect

Tenacity:  Brittle

Streak:  White or grayish white

Synonyms/varieties:

Comments: Found in sedimentary beds, as gangue mineral in ore veins, and in traprock zeolite occurrences. Worldwide occurrences where marine evaporite beds occur, often interbedded with halite.