an allotropic nonmetallic element, occurring free in volcanic regions and in combined state in gypsum, pyrite, and galena. The stable yellow rhombic form converts on heating to monoclinic needles. It is used in the production of sulphuric acid, in the vulcanization of rubber, and in fungicides. Symbol: S; atomic no: 16; atomic wt: 32.066; valency: 2, 4, or 6; relative density: 2.07 (rhombic), 1.957 (monoclinic); melting pt: 115.22°C (rhombic), 119.0°C (monoclinic); boiling pt: 444.674°C

(as modifier)