Chalcopyrite, pyrrhotite, pentlandite, and cubanite. Stillwater, Montana, USA

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Pentlandite (light brown, high reflectance, centre top) has well developed (111) cleavage and flame-like margins (top, centre) growing into pyrrhotite. It is surrounded by an intergrowth of chalcopyrite (yellow, top left) and cubanite, which shows reflection pleochroism from light red-brown (centre right) to lilac-grey (centre). Pyrrhotite (dark brown, top left, top and bottom centre) surrounds pentlandite and shows cleavage. Silicates are black.

Polished block, plane polarized light, x 160, oil

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