fluorite

fluorite or fluorspar , mineral appearing in various colors, e.g., green, yellow-brown, rose, and red. Chemically, it is calcium fluoride, CaF ₂ . Its crystals, commonly cubic, are transparent or translucent and under certain conditions exhibit fluorescence. The mineral also occurs in granular and massive forms. Fluorite is found in various parts of the world, especially in England, Germany, Mexico, and in Kentucky and Illinois in the United States. Its chief use is as a flux in metallurgy, but it is also employed in the preparation of hydrofluoric acid and in the manufacture of opal glass and enamel; some of its colorless crystals are used for making lenses and prisms.

fluorite Calcium fluoride crystal, used as an optical material. Objective lenses made from fluorite are particularly free from chromatic aberration, since fluorite has approximately half the dispersion of crown glass. Its drawbacks are that it is very expensive and is attacked by water, so fluorite elements must be sealed between other elements.