greigite

{{Infobox mineral | name = Greigite | image = Greigite structure 110 SFe4 tetrahedra.png | alt = | caption = Greigite structure, SFe4 tetrahedra | category = Sulfide mineral Thiospinel group Spinel structural group | formula = {{chem2|Fe^{2+}Fe^{3+}2S4}} | IMAsymbol = Grg | molweight = | strunz = 2.DA.05 | dana = | system = Cubic | class = Hexoctahedral (mm) H-M symbol: (4/m 2/m) | symmetry = Fdm | unit cell = a = 9.876 Å; Z = 8 | color = Pale pink, tarnishes to metallic blue-black | colour = | habit = Spheres of intergrown octahedra and as disseminated microscopic grains | twinning = | cleavage = | fracture = | tenacity = | mohs = 4 to 4.5 | luster = Metallic to earthy | streak = | diaphaneity = Opaque | gravity = 4.049 | density = | polish = | opticalprop = | refractive = | birefringence = | pleochroism = | 2V = | dispersion = | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | fusibility = | diagnostic = | solubility = | impurities = | alteration = | other = Strongly magnetic | prop1 = | prop1text = | references = }} Greigite is an iron sulfide mineral with the chemical formula {{chem2|Fe^{2+}Fe^{3+}2S4}}. It is the sulfur equivalent of the iron oxide magnetite (Fe3O4). It was first described in 1964 for an occurrence in San Bernardino County, California, and named after the mineralogist and physical chemist Joseph W. Greig (1895–1977).

==Natural occurrence and composition==