Pyrite, marcasite and sphalerite. Galapagos Mound, Pacific Ocean
Pyrite (light yellow) forms euhedral crystals, many with poorly crystalline cores (top right), or irregular banded poorly crystalline aggregates (brown-white, lower reflectance, top left). A thin rim of silica (grey, top left) encloses pyrite. Subhedral to euhedral sphalerite (light grey, bottom right) inclusions occur in pyrite. Radiating crystals of marcasite (white, centre) surround pyrite and show incipient alteration to limonite along growth zones. Black areas are polishing pits.
Polished block, plane polarized light, x 80, air