Sphalerite, chalcopyrite, pyrite and covelline. Parys Mountain, Britain

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Euhedral pyrite (light yellow-white, centre right) crystals occur within chalcopyrite (yellow, centre right) and sphalerite (light grey). fractures within chalcopyrite and sphalerite are infilled with covelline (deep blue, centre). Sphalerite shows extensive chalcopyrite disease, with chalcopyrite inclusions oriented along crystal boundaries, twin planes and growth zones (top right). Very fine-grained to submicroscopic chalcopyrite (centre) imparts a yellow-brown surface colour to sphalerite. Black areas are polishing pits.

Polished block, plane polarized light, x 80, air

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