Argentopyrite, rammelsbergite, pyrargyrite, safflorite and violarite. Tynebottom Mine, North Pennines, Britain

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This is the same field of view as 37b but with partially crossed polars. The anisotropy of argentopyrite (red, grey and orange, centre bottom) shows that much of it has sector twins (top centre). Rammelsbergite is also anisotropic (pink and purple) and shows polysynthetic twinning (bottom centre). Rhombic safflorite overgrowths show light blue and orange anisotropy colours (bottom centre). Pyrargyrite shows both anisotropy colours (light to dark blue, right centre) and strong red internal reflections which mask its anisotropy colours (centre top).

Polished block, plane polarized light, x 80, air

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