A mineral having composition CdS (cadmium sulfide) and crystallising in the hexagonal system (dihexagonal pyramidal class). Pyramidal crystals are rare, and greenockite usually occurs as earthy coatings with resinous lustre and yellow-to-orange color. There is good prismatic cleavage; the hardness is 3 (Mohs scale) and specific gravity is 4.9. Greenockite and wurtzite, ZnS, are isostructural, and a complete solid-solution series exists between the two minerals. Although greenockite is the most common cadmium mineral, no deposits of it are sufficiently large to warrant mining it solely as a source of cadmium. It is commonly associated with sphalerite, and thus the supply of cadmium comes as a by-product from the treating of zinc ores.