Pyrite, magnetite, chalcopyrite, pyrrhotite and covelline. El Salvador, Chile

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Coarse crystals of pyrite (yellow-white) carry abundant inclusions. These are euhedral magnetite (grey-brown, low reflectance, centre right), rounded pyrrhotite (brown, left centre, centre) and chalcopyrite (yellow, centre right). Mixed chalcopyrite-pyrrhotite inclusions (centre) are rarer than monophase inclusions. Chalcopyrite, which has altered to covelline (deep blue, centre bottom), has overgrown pyrite. Silicates are black areas. The association of pyrite with magnetite, pyrrhotite and chalcopyrite inclusions is common in many types of ore. Pyrrhotite-chalcopyrite inclusions are due to the unmixing of iss (intermediate solid solution).

Polished block, plane polarized light, x 160, oil

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