Sphalerite

Sphalerite, zinc sulfide, is and has been the principal ore mineral in the world. Zinc uses range from metal products to rubber and medicines. Zinc alloys readily with other metals and is chemically active. On exposure to air, it develops a thin gray oxide film (patina), which inhibits deeper oxidation (corrosion) of the metal. The metal’s resistance to corrosion is an important characteristic in its use. Zinc is also a necessary element for proper growth and development of humans, animals, and plants; it is the second most common trace metal, after iron, naturally found in the human body.

Sphalerite commonly contains minor amounts of other elements; cadmium, which shares certain similar chemical properties with zinc, will often substitute for zinc in the sphalerite crystal lattice. Cadmium is primarily consumed for the production of rechargeable nickel cadmium batteries; other end uses include pigments, coatings and plating, and as stabilizers for plastics. 

This specimen comes from Creede, Colorado