Celestine

Formula:  SrSO₄

Origin of name:  From Latin caelestis - sky (blue)

Crystal system:  Orthorhombic

Crystal class:  2/m 2/m 2/m

Twinning: 

Unit cell: a = 8.359 Ǻ, b = 5.352 Ǻ, c = 6.866 Ǻ

Colour:  Colourless, white, blue gray, green, yellow, red, brown

Diaphaneity:

Luster:  Vitreous

Habit:  Crystals thick to thick tabular, equant, or pyramidal, nodules, fibrous veinlets; massive granular, lamellar, earthy

Hardness:  3 to 3.5

Specific gravity:  3.97

Cleavage:  3; {001} perfect, {210} good, {010} indistinct

Tenacity:  Brittle

Streak:

Synonyms/varieties:  Celestite, cliftonite (impure var.)

Comments:  Sometimes fluoresces