Fluorspar
Fluorspar– fluoride subclass mineral, CaF2.
Sometimes Ca is substituted in a small amount by Y (yttrium-fluorite) or rare-earth elements such as (TR), Sr, Mn, Na, U.
It crystallizes in isometrical system, forming so-called fluorite structure (see crystal structure).
The crystals have the shape of a cube, octahedron and others; units are compact, coarse, grainy and earthy.
Hardness - 4; density - 3.2 g / cc.
Such an impurities as TR, U may color fluorspar in purple, green, yellow and
other colors.
Pure colorless fluorite is rare (valuable optical materials)
Polygenic mineral is used as a flux in metallurgy, raw material for hydrofluoric acid and its salts.
Mono crystals (mainly synthetic) are used in optics.