Chalcopyrite, pyrite and sphalerite. Neves-Corvo, Portugal
A relict of banded poorly crystalline (brown-yellow, lower reflectance, centre) and well crystalline (light yellow-white, centre top) pyrite has been fractured and extensively replaced by chalcopyrite (yellow), which carries rare small sphalerite (light grey, bottom right) inclusions. The brownish poorly crystalline pyrite is the so-called melnikovite pyrite. Black areas are polishing pits. Banding within the relict pyrite (centre left) shows little sign of disruption, suggesting that replacement was not accompanied by significant fracturing.
Polished block, plane polarized light, x 80, air