Cadmium resembles zinc in its chemical properties, and its occurrence for commercial purposes is with zinc ores. A relatively rare element in the Earth's crust, cadmium ranks in abundance between mercury and silver. Most cadmium occurs in solid solution in the zinc sulfide mineral called sphalerite. Although cadmium may be recovered from some lead and copper ores, it is associated with the zinc which is also found in these ores. Although a few zinc concentrates contain as much as 1–2% cadmium, typical content ranges from 0.06 to 0.5%. Since cadmium is entirely a by-product metal, the supply available is closely aligned with zinc production, averaging about 0.4% of zinc production.