Cryolite ... sodium aluminum fluoride
Crystallography: monoclinic
Colors: white , colorless
Luster: vitreous or pearly
Hardness: 2.5
Specific gravity: 2.95 - 3
Comments: used in pottery glazes and glass Cubic Zirconia...man made ...
Therefore, it is extracted by electrolysis; that is, the aluminium oxide is dissolved in molten cryolite and then reduced to the pure metal. By this process, the operational temperature of the reduction cells is around 950 to 980 °C.
It is found combined as calcium fluoride in fluorite, and as a double fluoride of aluminum and sodium in cryolite.
The yellow of Vaseline glass comes from uranium, first used in glass-making in the second half of the 19th century. The milky effect was obtained by adding a substance called cryolite and by careful reheating.
In modern production the opaque effect is created by adding calcium and sodium fluorides to the molten glass mix in the form of fluorine compounds such as cryolite or fluorine spar, as well as zinc oxide and alumina.
 See also: Crystal, Glass, Calcium, Rough, Fire
  
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