Sodalite

Formula: Na₈Al₆Si₆O₂₄Cl₂

Origin of name: from composition

Crystal system: cubic

Crystal class: -43m

Twinning: common on {111} penetration or repeated

Unit cell: a = 8.87 Å

Colour: colourless, white, yellowish, greenish, light to dark blue, red

Diaphaneity: 

Luster: vitreous to greasy

Habit: crystals dodecahedral, massive, embedded grains, nodules with concentric structure

Hardness: 5.5 to 6

Specific gravity: 2.14 to 2.4

Cleavage: 1; {110} poor

Tenacity: 

Streak: colourless

Synonyms/varieties: hackmannite (pink, Na-rich variety)

Comments: also from meteorites