Chalcopyrite, bornite, chalcocite, haematite and cassiterite. Wheal Jane, Cornwall, Britain

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Equant and prismatic cassiterite (dark grey-brown, well polished, centre) is intergrown with fine-grained haematite (light blue-grey, pitted, centre bottom). Chalcopyrite (yellow) is veined by bornite (brown, top right) and chalcocite (light blue, top left). Chalcocite also forms a rim around the oxide minerals. Black areas are polishing pits. A single crystal of cassiterite (top right) is present within the copper-iron sulphides. The cross-cutting relationships show that the alteration sequence is chalcopyrite to bornite to chalcocite.

Polished block, plane polarized light, x 80, air

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