Sphalerite, chalcopyrite, galena and pyrite. Rishi, Nigeria

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The main phase is sphalerite. Areas adjacent to fractures and those that contain abundant submicroscopic chalcopyrite inclusions have an anomalous red-brown surface colour (top left), whereas sphalerite with larger chalcopyrite (yellow) inclusions and few fine-grained chalcopyrite inclusions has a more characteristic grey colour (bottom right). A rounded galena crystal (white, centre) and small pyrite crystals (pale yellow, high reflectance, right centre) are intergrown with coarse chalcopyrite inclusions. Pyrite has been plucked from chalcopyrite (left centre). Black areas are silicate gangue. The anomalous sphalerite areas show anisotropy effects in crossed polars and have suffered extensive chalcopyrite disease the replacement of sphalerite by chalcopyrite.

Polished block, plane polarized light, x 80, air

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