Pyrite, native gold and galena. Clogau Mine, Wales, Britain




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250µm


A pyrite crystal (green-white) has an outer growth zone of poorly crystalline pyrite with lower reflectance itself overgrown by later euhedral pyrite (centre right). Pyrite carries inclusions of native gold (yellow, high reflectance, top left) and galena (blue-grey, centre). Black areas are quartz. The presence of the gold alters the perceived surface colour of the other minerals and lowers their apparent reflectance. The gold is 800 fine.


Polished block, plane polarized light, x 80, air



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