Cryolite

An interesting feature of this mineral is that it "disappears" when immersed in water due to the similarity in refractive indices. It is named from two Greek words meaning "frost" and "stone", in allusion to its frosty appearance. Historically, it was used as an aluminum ore, and when bauxite became the ore of aluminum, cryolite was used as a flux in the electrolytic process.

Mineral Photos courtesy of R.Weller/Cochise College