Cryolite

Formula:  Na3AlF6

Origin of name:  From Greek for frost

 

Crystal system:  Monoclinic

Crystal class:  2/m

Twinning:  Common by at least 13 distinct twin laws, penetration or polysynthetic

Unit cell: a = 7.77 Å, b = 5.59 Å, c = 5.40 Å, β = 90.2°

 

Colour:  Colourless, white, golden yellow, brownish, reddish

Diaphaneity:

Luster:  Vitreous to greasy

Habit:  Crystals cuboidal or short prismatic; massive, coarse granular

Hardness:  2.5

Specific gravity:  2.97

Cleavage:  2; {001} and {110} parting

Tenacity:  Uneven; brittle

Streak:  White

 

Synonyms/varieties:

 

Comments:

 

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