Pyrite, uraniferous carbon (thucholite), coffinite, zircon, TiO2 minerals, uraninite, chalcopyrite and pyrrhotite. Vaal Reef, Witwatersrand, Republic of South Africa




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250µm


Rounded pyrite grains (light yellow-white) are heavily fractured (centre) and contain small chalcopyrite (yellow, bottom centre) inclusions. One pyrite grain (top left) comprises recrystallized framboids and above it a rounded detrital grain has an (?)authigenic pyrite overgrowth separated by a thin silicate-rich zone. Uraniferous carbon, also known as thucholite (brown-grey, centre right), contains small square shaped uraninite (light grey) crystals in its centre. The carbon shows faint reflection pleochroism and bireflectance. The carbon is surrounded by a coffinite-rich area (light grey, centre top) enclosing pyrite. Acicular crystals of TiO2 (light grey, bottom centre) form a leucoxene aggregate and have higher reflectance than coffinite and zircon (dark grey, bottom right) which is also fractured. Two euhedral crystals of pyrrhotite (brown-yellow, bottom left) have nucleated upon a detrital pyrite grain.


Polished block, plane polarized light, x 80, air



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