Zinc is the 23rd most abundant element in the earth's crust. Sphalerite, zinc sulfide, is and has been the principal ore mineral in the world. In the United States, about two-thirds of zinc is produced from ores (primary zinc) and the remaining one-third from scrap and residues (secondary zinc). Zinc is necessary to modern living, and, in tonnage produced, stands fourth among all metals in world production - being exceeded only by iron, aluminum, and copper. Zinc uses range from metal products to rubber and medicines. About three-fourths of zinc used is consumed as metal, mainly as a coating to protect iron and steel from corrosion (galvanized metal), as alloying metal to make bronze and brass, as zinc-based die casting alloy, and as rolled zinc. The remaining one-fourth is consumed as zinc compounds mainly by the rubber, chemical, paint, and agricultural industries. 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.