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