Greenockite

Greenockite is a cadmium sulfide mineral with the chemical formula CdS. It is the natural mineral form of cadmium sulfide and occurs in hydrothermal veins and replacement deposits, frequently in association with sphalerite, galena, quartz and calcite. The mineral is named after Greenock, Scotland, the locality where it was first described.

Color ranges from yellow to orange-brown; crystals are typically small and may be prismatic or tabular; it occurs as granular masses as well. The luster is resinous to greasy, and transparency ranges from transparent to opaque. CdS can crystallize in two forms: hexagonal wurtzite and cubic sphalerite; greenockite samples are commonly hexagonal.

Physical properties include a Mohs hardness of about 3.5–4 and a specific gravity near 4.8. It is relatively rare compared with more abundant zinc and lead minerals and is most often recovered as a minor product in the processing of zinc-bearing ores rather than as a primary cadmium ore.

Cadmium produced from zinc ore is often linked to greenockite, but the mineral itself is not a major ore deposit. Cadmium is toxic, so handling and ore processing require care. Beyond its role as a cadmium source, CdS is notable as a semiconductor and as a pigment historically used as cadmium yellow.