CRYOLITE

This article appears in Volume V07, Page 562 of the Encyclopedia Britannica.

Encyclopedia Britannica - Main :: CRE-DAH

CRYOLITE , a

mineral

MINERAL

discovered in Greenland by the Danes in 1794, and found to be a compound of fluorine, sodium and

aluminium

ALUMINIUM (symbol Al; atomic weight 27.0)

. From its general

appearance

APPEARANCE (from Lat. apparere, to appear)

, and from the fact that it melts readily, even in a candle-flame, it was regarded by the Eskimos as a peculiar kind of ice; from this fact it acquired the name of cryolite (from Gr. icpboc, frost, and ki.Bos, stone). Cryolite occurs in colourless or snow-white cleavable masses, often tinted brown or red with iron

oxide

OXIDE

, and occasionally passing into a black variety. It is usually translucent, becoming nearly transparent on immersion in water. The

mineral

MINERAL

cleaves in three rectangular directions, and the crystals occasionally found in the crevices have a cubic habit, but it has been proved, after much discussion, that they belong to the anorthic system. The hardness is 2.5, and the specific gravity 3. Cryolite has the

formula

Na3AIF6, or 3NaFAlF3, corresponding to fluorine 54.4, sodium 32.8, and

aluminium

ALUMINIUM (symbol Al; atomic weight 27.0)

12.8%. It colours a flame yellow, through the presence of sodium, and when heated with sulphuric acid it evolves hydrofluoric acid.
Cryolite occurs almost exclusively at Ivigtut (sometimes written Evigtok) on the Arksut Fjord in S.W. Greenland. There it forms a large deposit, in a granitic vein running through gneiss, and is accompanied by quartz, siderite, galena,

blende

BLENDE, or SPHALERITE

, chalcopyrite, &c. It is also associated with a group of kindred minerals, some of which are evidently products of alteration of the cryolite, known as pachnolite, thomsenolite, ralstonite, gearksutite, arksutite, &c. Cryolite likewise occurs, though only to a limited extent, at Miyask, in the Ilmen Mountains; at Pike's

Peak

PEAK, THE

, Colorado, and in the Yellowstone Park.
Cryolite is a mineral of much economic importance. It has been extensively used as a source of metallic aluminium, and as a flux in smelting the metal. It is largely employed in the manufacture of certain sodium salts, as suggested by Julius Thomsen, of

Copenhagen

COPENHAGEN (Danish Kjobenhavn)

, in 1849; and it has been used for the production of certain kinds of

porcelain

PORCELAIN

and glass, remarkable for its toughness, and for enamelled

ware

WARE

.
Although cryolite is known as ice-stone " (Eisstein), it is not to be confused with "ice-spar" (Eisspath), which is a vitreous kind of felspar termed " glassy felspar" or
rhyacolite_ (F. W. R.*)

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