Uranium vein association

Uraninite, pyrite, chalcopyrite and safflorite. Tyndrum, Scotland

Uraninite (light, grey-brown, top) shows collomorphic banding along its margins (top left), seen by slight variations in reflectance. Pyrite (light yellow-white) is poorly crystalline (top right, bottom right), whereas marcasite (white, bottom centre) is well polished and has a poorly developed lath-shaped habit. Anhedral chalcopyrite (yellow, top right) is common. The discrete crystal rim (white, centre left) has the habit of a replaced safflorite. Gangue silicates are dark grey, black areas are polishing pits.

Polished thin section. plane polarized light, x80, air

Uraninite, galena and chalcopyrite. Tyndrum, Scotland

Distinctly botryoidal uraninite shows growth zones with different reflectances and surface colours (top). It encloses abundant anhedral galena (white, top) inclusions. Present in the gangue are small chalcopyrite (yellow, top left) inclusions. Locally, the gangue shows red internal reflections (top right) due to the presence of very fine-grained haematite.

Polished thin section, plane polarized light, x 160, oil

Uraninite and chalcopyrite. Tyndrum, Scotland

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

Uraninite and chalcopyrite. Port Radium, Northwest Territories, Canada

Coarse botryoidal uraninite (light grey, bottom) is accompanied by smaller botryoidal uraninite, 'blasenblende' (top). Chalcopyrite (yellow, centre bottom) lies along fractures and shrinkage cracks of the uraninite. The carbonate gangue shows bireflectance (top left).

Polished block, plane polarized light, x 40, air

Uraninite and chalcopyrite. Port Radium, Northwest Territories, Canada

Botryoidal, collomorphic uraninite (light grey, centre) encloses a rhombic carbonate (dark grey, centre). Fine-grained chalcopyrite (yellow, centre bottom) is abundant within uraninite. The carbonate gangue shows bireflectance (light and darker grey, top). Grey area (bottom) is resin.

Polished block, plane polarized light, x 40, air

Uraninite, carbonaceous matter and chalcopyrite. Port Radium, Northwest Territories, Canada

Uraninite (light grey, left) forms coarse botryoidal aggregates and smaller 'blasenblende' (bottom centre) and contains chalcopyrite (yellow, top centre), often along shrinkage cracks. Coarse carbonaceous matter (brown-grey, top right) shows faint bireflectance and reflection pleochroism (brown-grey to grey, right centre). The carbonate gangue (dark greys) shows cleavage, polysynthetic twinning (centre top) and bireflectance.

Polished block. plane polarized light, x 40, air