Cryolite Composition,
Crystallization & Structure

Composition. A fluoride of sodium and aluminum, Na3A1F6 = Fluorine 54,4 aluminum 12.8, sodium 32.8.

Crystallization. Monoclinic. Prominent forms are prism and base. Crystals rare, usually cub in aspect, and in parallel grouping growing out of massive material.

Structure. Usually massive.

Physical Properties. H. = 2.5. G. = 2.95-3. Vitreous to greasy luster. Colorless to snow-white. Transparent to translucent. A low index of refraction, giving the mineral an appearance of watery show or of paraffin. Powdered mineral almost disappears when immersed in water.

Test. Easily fusible (1.5) with strong yellow sodium flame. After intense ignition, residue fives alkaline reaction on moistened test paper. Fused in C.TG. with potassium bisulphate, evolves hydrofluoric acid and gives a volatile white ring of silica. Characteristic by its massive structure, white color and peculiar luster.

Occurrence. Occurs in a large vein lying in granite at Arksukfiord on the west coast of Greenland. The following minerals are found in small amounts associated with the cryolite: quartz, siderite, galena,. Sphalerite, pyrite, chalcopyrite, wolframite, fluorite, cassiterite, molybdenite, arsenopyrite, columbite. Found also in very small amounts at Miask, Ilmen Mountains, Siberia, and at foot of Pike’s Peak, Colorado.

Name. Name is derived from two Greek words meaning frost and stone, in allusion to its icy appearance.

Use. It is used for the m manufacture of sodium slats, of certain kinds of glass and porcelain, and as a flux in the electrolytic process for the production of aluminum.