Fluorite

Fluorite is calcium fluoride, CaF₂. It crystallizes in cubes, octahedra or combinations of both, in purple, green, blue, yellow, pink or colorless, often in color zones within one crystal. It cleaves perfectly in four directions, and many octahedra on the market are cleaved rather than grown. Fluorite gave fluorescence its name: many crystals glow blue under ultraviolet light. Classic localities include Weardale in England, Berbes in Asturias, the Elmwood Mine in Tennessee and the pink octahedra of the Alps. Since the 1990s China has supplied much of the market, with fluorite from Xianghualing and Yaogangxian in Hunan and from Inner Mongolia. Fluorite is soft, and its edges chip easily along the cleavage.