DIRK WIERSMA / SCIENCE PHOTO LIBRARY DIRK WIERSMA / SCIENCE PHOTO LIBRARY
Twinned augite crystals, polarised light micrograph. This mineral contains calcium, sodium, magnesium, iron and aluminium in a silicate matrix. Its crystals form in igneous rocks (black) such as potash-rich lavas. Augite is a member of the pyroxene group of rock-forming minerals. This cluster of crystals is around 8 millimetres across.
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