Galena (chemical formula PbS) is a gray mineral of metallic luster and is the main source of lead in Trepča. In appearance, pyrite (FeS2) and chalcopyrite (CuFeS2) resemble gold. Chalcopyrite is as important as copper ore. This druse also carries transparent prismatic crystals of quartz (SiO2), one of the most abundant minerals in the continental crust of our planet.