Sulfur (atomic number 16, symbol S) is a nonmetallic, crystalline solid element, commonly pale yellow in its pure form, vital for all life, though its compounds like hydrogen sulfide are toxic. It is an essential component of amino acids and vitamins in humans and is used industrially to make sulfuric acid, in vulcanizing rubber, and as a preservative. Sulfur is found in volcanic areas, sulfide and sulfate minerals (like gypsum), and is obtained through processes like the Frasch process.Â