Fluorite or fluorspar (calcium fluoride, CaF2) is a mineral that occurs in Derbyshire, crystallising either in cubes, octahedrally, or in compact masses like marble. It is also called Derbyshire spar, or when the crystals have a blue or purple hue, Blue John.
Fluorspar was described by Agricola in the 1st Century AD, as fluor (from the Latin fluo -I flow), since it melts at a red heat. As well as having been used in the production of decorative objects, Fluorspar is also used as a flux material in the smelting of iron and steel. It is also used as a source of fluorine and hydrofluoric acid and in the manufacture of ceramics and in the optical-glass industry.