Fe3S4

Fe3S4, commonly known as greigite, is an iron sulfide mineral with the chemical formula Fe3S4. It is a ferrimagnetic material with a spinel-like crystal structure in which iron exists in mixed valence states and sulfide ions form a three-dimensional lattice. Natural greigite occurs in reducing environments, including marine and lacustrine sediments, hydrothermal vents, and magnetic sediments, and is also produced by magnetotactic bacteria as a biomineral. It forms by the transformation of other iron sulfides under diagenetic conditions or by precipitation from sulfide-rich fluids.

Greigite is typically black to brownish-black and is sensitive to oxidation; when exposed to air it can alter to iron oxides or sulfates. It is sparingly soluble in acids and is generally insoluble in water. In terms of magnetism, greigite exhibits ferrimagnetic order at ambient temperatures, making it of interest in studies of magnetism and paleomagnetism as a potential recorder of ancient magnetic fields.

Synthetically, Fe3S4 can be prepared via controlled chemical reactions or electrochemical routes, yielding nanoscale or bulk forms for research. While it has attracted attention for its magnetic properties and potential spintronic applications, greigite has limited commercial use due to its instability and synthesis constraints.