Chalcopyrite and pyrite. Lasail, Oman
Chalcopyrite (yellow, right) surrounds poorly crystalline, fine-grained pyrite (brown, bottom centre) which has well crystalline margins (pale yellow-white, centre). The fine-grained nature of pyrite lowers its reflectance and gives a characteristic brown surface colour. The fine pyrite could be primary or altered pyrrhotite, but here it is probably primary. The gangue phases (dark grey) are silicates.
Polished block, plane polarized light, x 80, air