CRYOLITE
Cryolite is a rare sodium aluminofluoride (Na3AlF6).
Its name ("ice-rock") refers to its ~resemblance to ice in terms of
luster and low index of refraction (= a measure of how light passes through a
material, in terms of how much the light gets bent and the light’s change of
speed). Cryolite has a nonmetallic luster, a clear to white color, cubic
parting (not cubic cleavage), and a dull glassy luster.
Cryolite used to have considerable economic
significance, as it was used as a flux in making aluminum metal. The only
exploitable cryolite occurrence on Earth is (was) in southern Greenland's Gardar
Igneous Province at Ivigtut (aka Ivittuut). Ivigtut cryolite
was first mined in the 1850s, and that deposit is now ~exhausted.
Aluminum metal production nowadays uses artificially-made sodium
aluminofluoride flux.
Cryolite
(7.1 cm across) from Ivigtut, southwestern Greenland, the only significant
cryolite occurrence on Earth. This deposit is a cryolite body of igneous
origin within the roof zone of the Ivigtut Granite (mid-Mesoproterozoic,
1.171 billion years), a pipe-shaped intrusion penetrating an intrusion breccia
unit. In addition to cryolite, ten other very rare aluminofluoride
minerals have been reported from the Ivigtut Deposit.
Some
info. from:
Pauly
& Bailey (1999) - Genesis and evolution of the Ivigtut cryolite deposit, SW
Greenland. Meddelelser om Grønland, Geoscience 37. 60 pp.