Chalcopyrite and covelline. El Salvador, Chile
Anhedral chalcopyrite (yellow) has been replaced by covelline (dark blue) along crystal boundaries and cleavage. The gangue comprises coarse crystals of quartz (dark grey, bottom right) and euhedral basal sections and tabular crystals of tourmaline (higher reflectance, centre). Black areas are polishing pits.
Polished block, plane polarized light, x 80, air