Pyrite, chalcopyrite and sphalerite. Bayda, Oman
Euhedral pyrite (light yellow-white) crystals are extensively replaced by chalcopyrite (yellow) along the (100) cleavage directions of pyrite. Although pyrite is fractured, much of the chalcopyrite is replacing, rather than cementing, pyrite. Sphalerite (light grey, bottom centre) overgrows pyrite as small subhedral crystals (right centre) and is inclusion-free. Quartz is the main gangue phase (dark grey, top centre).
Polished block, plane polarized light, x 80, air