Ironsulfur

Iron sulfide compounds, collectively referred to as ironsulfur, are chemical compounds composed of iron and sulfur. In mineralogy, the term most often denotes iron sulfide minerals such as pyrite (FeS2), marcasite (FeS2 polymorph), troilite (FeS), and pyrrhotite (Fe1−xS). The broader category also includes binary compounds such as iron(II) sulfide (FeS) and iron disulfide (FeS2) and related phases like greigite (Fe3S4).

Natural iron sulfides form under reducing conditions in sedimentary, hydrothermal, and magmatic environments. Pyrite is the best-known example and is widely distributed in rocks and ore deposits. Marcasite is a polymorph that is less stable at surface conditions. Troilite occurs in meteorites and planetary materials, while pyrrhotite appears in many igneous rocks and can be magnetic. Non-stoichiometric Fe1−xS is also common in sulfide-rich rocks.

Physical properties vary among the minerals. Pyrite and marcasite share the FeS2 composition but have different crystal structures; pyrite is cubic, marcasite orthorhombic. Pyrrhotite tends to be more variable in composition and is often magnetic. When exposed to air and water, iron sulfides oxidize to iron oxides and sulfuric acid, a process linked to acid mine drainage in some settings.

Applications and research focus on ironsulfur include their role as ore minerals for iron and sulfur, and the use of synthetic iron sulfides in energy storage, catalysis, and magnetic materials. Pyrite has historically been used as pigment and ore, while greigite and related sulfides are studied for their magnetic properties.

Safety and environmental considerations include the potential for acid drainage from oxidizing sulfides and hazards associated with fine powders that may release gases under certain conditions.