Sulfur, Native

a mineral, one of the native elements. The two polymorphic modifications of sulfur, namely, orthorhom-bic α-sulfur and monoclinic β-sulfur, exist in nature. At atmospheric pressure and a temperature of 95.6°C, α-sulfur converts to β-sulfur. Native sulfur usually occurs as α-sulfur, which forms dipyramidal or, less frequently, thick prismatic crystals, as well as compact cryptocrystalline and, less frequently, powdery aggregates. The mineral is yellow, but in the presence of impurities the color varies from brown to black. Native sulfur has bitumens, carbonates, sulfates, and clays as inclusions. The mineral’s luster varies from resinous to greasy. Native sulfur has a hardness on Mohs’ scale of 1–2 and a density of 2,050–2,080 kg/m³. A brittle mineral, sulfur melts at 119°C and ignites at 214°–165°C.

The major types of native sulfur deposits are the volcano-genic and the exogenic. Exogenic deposits, which predominate, are associated with gypsum-anhydrite masses. These masses, under the action of the separation of hydrocarbons and hydrogen sulfide, are reduced and replaced by sulfur-calcite ores. All major deposits have infiltration and metasomatism genesis of this kind. Native sulfur is often formed (with the exception of larger accumulations) as a result of the oxidation of H₂ S. The geochemical processes for the formation of native sulfur are to a great extent activated by microorganisms (sulfate-reducing bacteria and thiobacteria). The most important volcanogenic deposits are the hydrothermal metasomatic deposits, such as those in Japan, formed by sulfur-bearing quartzites and opal-ites, and the deposits made up of volcanogenic, sedimentary sulfur-bearing silts of crater lakes.