Uraninite and chalcopyrite. Tyndrum, Scotland
125µm
Collomorphic banding in uraninite is seen as variations in surface colour and reflectance (centre top). Later, uraninite, overgrowing the main banded uraninite, is being replaced by secondary uranium-bearing phases (grey, reflectance similar to the gangue, centre top). Trace amounts of chalcopyrite (yellow, top left) are present. The gangue shows strong light-coloured internal reflections.
Polished thin section, plane polarized light, x 160, oil
