PASCAL GOETGHELUCK / SCIENCE PHOTO LIBRARY PASCAL GOETGHELUCK / SCIENCE PHOTO LIBRARY
Barite and chalcopyrite crystals. 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. Chalcopyrite, or copper iron sulphide, is one of the most widespread and important copper ores. It occurs both as grains in a host rock, as seen here, and also in vein-type deposits. It has a golden colour, but the surface tarnishes rapidly upon exposure to air leaving a characteristic iridescent film. This sample, from France, is 12 centimetres long.
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