Monosulfide

Monosulfide is a term used in mineralogy and inorganic chemistry to describe compounds that contain exactly one sulfur atom per formula unit, typically with the formula MS. In geology and mineral science, monosulfides refer to sulfide minerals with a 1:1 metal-to-sulfur ratio, though some non-stoichiometric members can occur (for example Fe1−xS, known as pyrrhotite).

Common examples of monosulfide minerals include troilite (FeS), nickel monosulfide (NiS), cobalt monosulfide (CoS), and manganese monosulfide (MnS). Zinc monosulfide (ZnS) is another well-known monosulfide, though its crystal chemistry can differ from transition-metal monosulfides. These minerals typically form in reducing environments such as igneous and metamorphic rocks, and they can also occur in meteorites and planetary interiors where sulfide liquids segregate from silicate melts.

Structurally, monosulfides often adopt close-packed metal substructures, with common arrangements including NiAs-type and rock-salt-type lattices, though the exact structure depends on the specific metal and temperature or pressure conditions. They are usually metallic or semiconducting in electrical behavior and can exhibit a range of physical properties from brittle to slightly malleable.

Economic and geological significance arises because monosulfides are important ore phases for metals such as nickel, cobalt, and iron. They can influence ore genesis, concentration, and processing, and they may undergo alteration or oxidation to sulfates in exposed environments. See also: disulfides, polysulfides, sulfide minerals, troilite.