Cadmium is a relatively rare element. Its abundance in the lithosphere is estimated at about 0.5 parts per million in the earth's crust. No cadmium has been found in commercial quantities, and no ore is mined solely for recovering cadmium. The most common mineral, greenockite (cadmium sulfide), occurs chiefly as a yellow stain or coating on zinc sulfide. Nearly all major zinc deposits contain cadmium in varying amounts, with the concentrates containing a maximum of about 1%.