Cryolite
Chemical compound
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Cryolite is an uncommon mineral identified with the once-large deposit at Ivittuut on the west coast of Greenland, mined commercially until 1987.
It is used in the reduction of aluminium, in pest control, and as a dye. Wikipedia
Formula: Na3AlF6
Melting point: 1012 °C
2V angle: 43°
Cleavage: None observed
Color: Colorless to white, also brownish, reddish and rarely black
Crystal class: Prismatic (2/m); (same H-M symbol)
Crystal habit: Usually massive, coarsely granular. The rare crystals are equant and pseudocubic