DIRK WIERSMA / SCIENCE PHOTO LIBRARY DIRK WIERSMA / SCIENCE PHOTO LIBRARY
Enargite mineral. The mineral enargite is a sulphide of copper and arsenic (Cu3.As.S4). Its crystal symmetry is orthorhombic pyramidal and it occurs as slender elongate crystals that are often striated. It may also form massive aggregates. Its colour is grey to blackish-grey, with a metallic lustre. This sample, from Butte, Montana, USA, is 8 centimetres across.
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