CRYOLITE

    Class : Halides
    Subclass : Fluorides
    Crystal system : Monoclinic
    Chemistry : Na3AlF6
    Rarity : Rare

Cryolite is a rare fluoride found in pegmatites. This mineral was the basis of the aluminum industry before the discovery of the bauxite transformation process by Ste-Claire Deville in the 19th century. It takes its name from the Greek kryos (cold) and lithos (stone), because of the resemblance of its crystals to ice. Cryolite sometimes forms large masses (6 meters at Ivigtut in Greenland) of a white, translucent hue accompanying siderite, microcline, topaz and other fluorides. Pseudocubic crystals with tri-rectangular cleavages are very rare and do not exceed 4 cm ; they usually form groups with parallel axes. Twins are common. Its role as a flux in the aluminum industry having now ended, cryolite no longer has any industrial application.

Main photo : Cryolite from Ivigtut Mine, Arsuk Fjord, Groenland © Kelly Nash

Cryolite in the World

The only cryolite deposit now exhausted was that of Ivigtut in Greenland. The Francon quarry (Montreal, Canada) also produced beautiful pseudo-octahedral yellow crystals measuring 4 cm. Cryolite is also reported as a curiosity in the pegmatites of the Urals (Miass), Colorado (Pikes Peak) and some other districts.

Photo on right : Cryolite from Poudrette quarry, Mont St-Hilaire, Canada © Modris Baum

Cryolite in France

Cryolite is not known in the French underground.

Twinning

Many twins are known (11 in total) for this mineral species.

Fakes and treatments

No fakes listed for this mineral species.


Hardness : 3 to 3.5
Density : 2.96 to 2.98
Fracture : Irregular
Streak : White

TP : Translucent to transparent
RI : 1.339 to 1.340
Birefringence : 0.001
Optical character : Biaxial +
Pleochroism : None
Fluorescence : Red

Solubility : Sulfuric acid


Magnetism : None
Radioactivity : None