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Previous to the recent discovery in Sardinia of cadmium oxide as small octahedral crystals, greenockite was the only known mineral containing cadmium as an essential constituent.

Sphalerite almost always contains a little cadmium, probably as the sulphide; and in zinc deposits crystals of sphalerite in cavities are frequently covered with a greenish-yellow film or coating of greenockite.

Cadmium occurs in nature as cadmium sulphide in greenockite, CdS, which is very rare.

It occurs in combination with sulphur in greenockite, and in some ores of zinc.

The zinc oxide minerals in the surficial zone also are sometimes colored yellow by small amounts of greenockite.