III.

Occurrence

Sulfur ranks about 16th in abundance among the elements in Earth's crust and is found widely distributed in both the free and combined states. In combination it occurs in many important metallic sulfides, such as lead sulfide, or galena, PbS; zinc blende, ZnS; copper pyrite, (Cu,Fe)S₂; cinnabar, HgS; stibnite, Sb₂S₃; and iron pyrite FeS₂. It is also combined with other elements in the form of sulfates such as barite, BaSO₄; celestite, SrSO₄; and gypsum, CaSO₄ · 2H₂O; and it is present in the molecules of many organic substances such as mustard, eggs, hair, proteins, and oil of garlic. In the free state it is found mixed with gypsum and pumice stone in volcanic regions throughout Iceland, Sicily, Mexico, and Japan, often occurring as a sublimate surrounding the volcanic apertures. Vast subterranean deposits are found in the United States in many parts of Louisiana and Texas, as well as in Colorado, Nevada, Wyoming, and California. Free sulfur may be formed from the weathering of pyrites or may be deposited by hot sulfurous waters in which hydrogen sulfide has been oxidized by the atmosphere. Annual U.S. production of elemental sulfur in the early 1990s amounted to about 10.6 million metric tons. During the same period, world production amounted to about 52.7 million metric tons.