FES

FeS, or iron sulfide, is the compound formed from iron and sulfide ions in a 1:1 ratio. In pure form it is a gray to black, metallic solid that can be brittle. In geology and mineralogy, FeS is most commonly encountered as two related materials: troilite, the stoichiometric mineral FeS, and pyrrhotite, a family of iron-deficient Fe1−xS phases. Troilite occurs in meteorites and Moon rocks and is a stable phase at low temperatures. Pyrrhotite occurs in many terrestrial rocks and shows variable iron content; it is often magnetic and can exist in multiple crystallographic variants.

Crystallography: Troilite adopts a hexagonal close-packed structure (NiAs-type). Pyrrhotite exhibits nonstoichiometric structures that depend on the iron vacancy concentration.

Chemical behavior: FeS is susceptible to oxidation in air, yielding iron oxides and sulfates. Finely divided FeS reacts with acids to release hydrogen sulfide, a toxic gas. It is also used as a laboratory model for sulfur chemistry and as a precursor in studies of iron–sulfur clusters.

Production and occurrence: In the laboratory, FeS can be prepared by direct combination of iron and sulfur at high temperature or by sulfidation of iron compounds under reducing conditions. In nature, FeS minerals form in reducing environments such as meteorite interiors, hydrothermal deposits, and some seafloor sediments.

Safety: Hydrogen sulfide release during acid reactions can be hazardous; powdered FeS dust may irritate the skin, eyes, and lungs.