Sulfur

sulfur crystals

sulfur (S), also spelled sulphur, nonmetallic chemical element belonging to the oxygen group (Group 16 [VIa] of the periodic table), one of the most reactive of the elements. Pure sulfur is a tasteless, odourless, brittle solid that is pale yellow in colour, a poor conductor of electricity, and insoluble in water. It reacts with all metals except gold and platinum, forming sulfides; it also forms compounds with several nonmetallic elements. Millions of tons of sulfur are produced each year, mostly for the manufacture of sulfuric acid, which is widely used in industry.

Explore boiling pots of molten sulfur at Nikko volcano near the Mariana IslandsSee all videos for this article

Explore the undersea molten sulfur deposit uncovered with a remotely operated vehicle near the Mariana Islands.See all videos for this article

In cosmic abundance, sulfur ranks ninth among the elements, accounting for only one atom of every 20,000–30,000. Sulfur occurs in the uncombined state as well as in combination with other elements in rocks and minerals that are widely distributed, although it is classified among the minor constituents of Earth’s crust, in which its proportion is estimated to be between 0.03 and 0.06 percent. On the basis of the finding that certain meteorites contain about 12 percent sulfur, it has been suggested that deeper layers of Earth contain a much larger proportion. Seawater contains about 0.09 percent sulfur in the form of sulfate. In underground deposits of very pure sulfur that are present in domelike geologic structures, the sulfur is believed to have been formed by the action of bacteria upon the mineral anhydrite, in which sulfur is combined with oxygen and calcium. Deposits of sulfur in volcanic regions probably originated from gaseous hydrogen sulfide generated below the surface of Earth and transformed into sulfur by reaction with the oxygen in the air.