Chloanthite, rammelsbergite, pyrargyrite, argentopyrite, acanthite and altered argentopyrite. Tynebottom Mine, North Pennines, Britain

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This section has been polished with ¼µm diamond paste but shows the effects of overpolishing. Chloanthite (cream-white) is overgrown by rhombic rammelsbergite (pale blue-white, slightly lower reflectance, centre) on the edge next to pyrargyrite. Pyrargyrite (blue) and argentopyrite (brown) overgrow the arsenides. In argentopyrite the slightly higher reflectance patches with a lighter surface colour in the centre of the crystals are more overpolished than the margins. The pyrargyrite crystal (bottom centre left) also shows the same effect. Acanthite (light blue-grey, bottom left) is less strongly coloured than pyrargyrite and more poorly polished. Fine-grained porous aggregates of pyrite, marcasite and an uncharacterized mineral, AgFe11S8, have pseudomorphed argentopyrite (bottom right) but individual crystals cannot be identified at this magnification. Calcite (dark grey) is the main gangue.

Polished block, plane polarized light, x 80, air

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