Well-developed crystals of pyrite, sphalerite and quartz on an igneous rock substrate. The dark, lustrous crystals are of sphalerite, a zinc-sulphide with varying content of iron, chemical formula (ZnFe)S. Sphalerite is a common ore of zinc. Quartz in this sample occurs as thin and clear elongate prisms, while the lustrous metallic pyrite may partially consist of marcasite and pyrrhotite. Sample is from the Trepca mine in Kosovo. See pencil for scale.