Fluorite

from WordNet (r) 3.0 (2006)

fluorite
    n 1: a soft mineral (calcium fluoride) that is fluorescent in
         ultraviolet light; chief source of fluorine [syn:
         {fluorite}, {fluorspar}, {fluor}]

from The Collaborative International Dictionary of English v.0.48

Fluorite \Flu"or*ite\, n. (Min.)
   Calcium fluoride ({CaF2}), a mineral of many different
   colors, white, yellow, purple, green, red, etc., often very
   beautiful, crystallizing commonly in cubes with perfect
   octahedral cleavage; also massive. It is used as a flux. Some
   varieties are used for ornamental vessels. Also called {fluor
   spar}, or simply {fluor}.
   [1913 Webster]