Pyrite, chromite, altered uraninite, rutile and zircon. Vaal Reef, Witwatersrand, Republic of South Africa

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Rounded pyrite grains (yellow-white) are heavily fractured and carry pyrrhotite and chalcopyrite inclusions (top left) which cannot be distinguished from each other at this magnification. A rounded chromite (light grey, bottom centre right) has a zircon (dark grey, lower reflectance than chromite, bottom centre) lying between it and the adjacent shattered pyrite. Lying above two small chromite crystals (bottom right) is an extensively altered uraninite grain (diffuse lighter grey patch) containing very fine-grained chalcopyrite and galena (higher reflectance 'spots'). Small rutile crystals (light grey) occur within a pyrite grain or surround it (centre top). Quartz is dark grey.

Polished block, plane polarized light, x 80, air

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