PASCAL GOETGHELUCK / SCIENCE PHOTO LIBRARY PASCAL GOETGHELUCK / SCIENCE PHOTO LIBRARY
Fluorite (purple) and barite (brown) crystals. Fluorite, or fluorspar (calcium fluoride) is a fairly common mineral, extensively mined for use in steelmaking (as a flux) and in other industrial processes. It occurs in cubic crystal groups that can vary in colour from soft green and yellow to colourless and deep purple. Barite, or barium sulphate, is a very common mineral. It is used in the oil, paper and rubber industries and is the principal ore for barium. Barium meals and enemas are used in radiography. This sample, from France, is 11 centimetres wide.
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