Cryolite

Lore & Background

The name is derived from the Greek words cryos (frost) and lithos (stone). The Pennsylvania Salt Manufacturing Company used large amounts of cryolite to make caustic soda and fluorine compounds, including hydrofluoric acid at its Natrona, Pennsylvania, works, and at its integrated chemical plant in Cornwells Heights, Pennsylvania, during the 19th and 20th centuries. It was historically used as an ore of aluminium and later in the electrolytic processing of the aluminium-rich oxide ore bauxite. The difficulty of separating aluminium from oxygen in the oxide ores was overcome by the use of cryolite as a flux to dissolve the oxide mineral(s). According to economist Arindam Banerjee, exploitation of cryolite in Greenland contributed nearly 54 billion euros to Danish economy, though this claim has been strongly disputed.

Reader's Guide

Cryolite's primary historical significance lies in its role as a flux in the Hall–Héroult process for refining aluminium. Although natural cryolite is now too rare for this purpose, synthetic sodium aluminium fluoride produced from fluorite has replaced it. The mineral also found use as an insecticide, pesticide, a yellow colorant in fireworks, and as an opaliser in glass manufacturing. Its unique physical property of having a refractive index close to water makes it nearly invisible when immersed. The Ivittuut deposit in Greenland was the world's only commercial source, and its protection during World War II underscored its strategic importance.

Did You Know?

• Cryolite becomes essentially invisible when immersed in water due to its refractive index of about 1.34.
• It was first described from rock samples obtained from Inuit who used it for washing hides.