The quarry is also noted for crystals of greenockite. Greenockite (CdS), the only cadmium mineral of importance, is nearly always associated with sphalerite (ZnS). The only cadmium mineral of importance, greenockite (CdS), is nearly always associated with sphalerite (ZnS). Greenockite belongs to the wurtzite group and is isostructural with it at high temperatures. Greenockite is a rather rare species, considering it has a very simple chemistry (cadmium sulfide).