Fluorite

Calcium fluoride, 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.

a soft mineral (calcium fluoride) that is fluorescent in ultraviolet light; chief source of fluorine