Wollastonite

Formula: CaSiO₃

Origin of name: for W. Wollaston, English mineralogist

Crystal system: triclinic

Crystal class: -1

Twinning: common on {100} about [010] axis

Unit cell: a = 7.93 Å, b = 7.32 Å, c = 7.06 Å, a = 90.1°, b = 95.2°, g = 103.4°

Colour: white to grayish, colourless, pale green

Diaphaneity: 

Luster: vitreous to pearly, somewhat silky if fibrous

Habit: crystals tabular, massive, cleavable to fibrous or granular and compact

Hardness: 4.5 to 5

Specific gravity: 2.87 to 3.09

Cleavage: 3; {100} perfect, {001} and {-102} good

Tenacity: splintery

Streak: white

Synonyms/varieties: grammite

Comments: data for wollastonite-2M, there are also -1A, -3A, -4A, -5A and -7A polytypes, sometimes fluoresces