Pyrite, arsenopyrite, sphalerite and chalcopyrite. English Lake District, Britain
Euhedral rhombic arsenopyrite (white, right) has higher reflectance than pyrite (light yellow, bottom left). Sphalerite (light grey) occurs as rare inclusions in arsenopyrite (top right) but mainly as large aggregates (bottom) with abundant crystallographically oriented chalcopyrite inclusions (chalcopyrite disease). Dark grey areas are chlorite-rich gangue.
Polished block, plane polarized light, x 40, air