Chalcocite, bornite and pyrite. Levant Mine, Cornwall, Britain
Chalcocite (blue) has a symplectite-like intergrowth with bornite (brown, centre right). Euhedral to subhedral pyrite (light yellow-white, centre bottom) shows relief against chalcocite and its irregular shape suggests that it has been partially replaced by chalcocite.
Polished block, plane polarized light, x 80, air