Bornite, stromeyerite, chalcocite, pyrite and tetrahedrite group mineral. Unknown Provenance
250µm
This section has been polished with ¼ µm diamond paste. Although the section is scratch-free has enormous relief and hence shows strong shadows about the harder phases. Euhedral to subhedral pyrite (pale yellow, high reflectance), a tetrahedrite group mineral (light grey, centre and top centre) and quartz (dark grey, bottom centre) show high relief against the softer copper and silver sulphides. Bornite (brown-red, left) has an symplectite-like intergrowth with, and inclusions of, chalcocite (light blue). Stromeyerite (light lilac-grey, centre right) also is complexly intergrown with chalcocite. Although relief accentuates the symplectite texture of the softer phases, they remain poorly polished in areas close to high relief minerals. Minerals forming thin rims around the harder phases would be 'lost' within the shadows. Bornite (top and bottom right) is purple coloured rather than brown, this is tarnish which has been protected by the adjacent quartz crystals from removal.
Polished block, plane polarized light, x 80, air
