Fluorapatite

Formula:  Ca₅(PO₄)₃F

Origin of name:  From fluorine member of apatite group

Crystal system:  Hexagonal

Crystal class:  6/m

Twinning:  Rare on {11-21}, contact; rare on {10-13}; also on {10-10} or {11-23}

Unit cell: a = 9.368 Ǻ, c = 6.884 Ǻ

Colour:  Colourless, white, gray, yellow to yellowish green, green, blue

Diaphaneity:

Luster:  Vitreous to subresinous, silky

Habit:  Crystals short to long prismatic, thin to thick tabular or complex; massive compact to coarse granular; fibrous

Hardness:  5

Specific gravity:  3.1 to 3.2

Cleavage:  2; {0001} indistinct, {10-10} trace

Tenacity:  Conchoidal to uneven; brittle

Streak:  White

Synonyms/varieties:  Chrysolite, collophane (massive, amorphous var.), odontolite

Comments:  Often fluoresces, phosphorescent in UV light, or thermoluminescent