Cryolite
Image: Robert M. Lavinsky (CC BY-SA 3.0)
Mineral NameCryolite
Chemical FormulaNa3AlF6
Mohs Hardness2.5
Crystal Systemcubic
Lustervitreous
Streak ColorWhite
CleavagePoor/imperfect in three directions (pseudo-cubic)
FractureUneven to conchoidal
Specific Gravity2.95
Colorscolorless, white, reddish-brown, black
TransparencyTransparent to translucent
Type LocalitySt Peters Dome, Cheyenne District (St. Peters Dome District), El Paso County, Colorado, USA
Mineral GroupHalides
Usesflux in aluminum production (historically), insecticide, collector's mineral
Associated Mineralsquartz, fluorite, siderite, galena, chalcopyrite, sphalerite
Rarityvery-rare
Description
This specimen displays a blocky, white to colorless, translucent mass of cryolite, exhibiting its characteristic greasy to vitreous luster. The mineral often forms pseudo-cubic crystals, though this sample appears more massive.
Geological Context
Cryolite is a rare halide mineral typically found in granite pegmatites and alkaline igneous rocks, forming during late-stage hydrothermal processes. The most significant historical deposit was Ivittuut, Greenland, where it occurred in a large pegmatite body.
