"Cryolite Corporation Danmark"
Cryolite mine in Greenland, 1940
Public DomainCryolite mine in Greenland, 1940

Cryolite is a glassy, colourless and very uncommon mineral found in large quantities only in one place in the world: on the west coast of Greenland.  However the deposit there ran out in 1987. Smaller quantities have been reported in Colorado, Quebec, Russia and few other places.

It is used in the production of aluminium.