Covelline, bornite, haematite, wittichenite and arsenopyrite. English Lake District, Britain

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Digenite has been totally replaced by fine-grained covelline which shows reflection pleochroism from dark to light blue (centre). Only the cleavage of digenite shows its former presence. Bornite (orange-brown) and minor wittichenite (cream, top centre) surround covelline and are rimmed by fine-grained haematite (green-grey, top left). A euhedral crystal of arsenopyrite (white, high reflectance, centre) occurs within covelline. Dark grey areas are quartz crystals (top left). Black areas are polishing pits.

Polished block, plane polarized light, x 80, air

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