Pyrite, arsenopyrite, sphalerite, chalcopyrite and galena. English Lake District, Britain
Euhedral rhombic arsenopyrite (white, high reflectance, centre), showing faint reflection pleochroism (centre right), is enclosed within a fine-grained mosaic of pyrite (light yellow). Sphalerite (light grey, bottom left) has abundant chalcopyrite (yellow) inclusions in its cores but has inclusion-free rims (bottom left). Quartz gangue (top right) is dark grey.
Polished block, plane polarized light, x 40, air