Iron(II,III) oxide is the chemical compound with formula Fe3O4. It occurs in nature as the mineral magnetite. It is one of a number of iron oxides, the others being iron(II) oxide (FeO), which is rare, and iron(III) oxide (Fe2O3) also known as hematite. It contains both Fe2+ and Fe3+ ions and is sometimes formulated as FeO ∙ Fe2O3. This iron oxide is encountered in the laboratory as a black powder. It exhibits permanent magnetism and is ferrimagnetic, but is sometimes incorrectly described as ferromagnetic.
Molar mass：231.533 g/mol
Appearance：solid black powder
Melting point：1,597 °C (2,907 °F; 1,870 K)
Boiling point：2,623°C (4,753 °F; 2,896 K)
Refractive index (nD)：2.42
Fe3O4 is used as a black pigment and is known as C.I pigment black 11 (C.I. No.77499) or Mars Black.
Fe3O4 is used as a catalyst in the Haber process and in the water-gas shift reaction. The latter uses an HTS (high temperature shift catalyst) of iron oxide stabilised by chromium oxide. This iron–chrome catalyst is reduced at reactor start up to generate Fe3O4 from α-Fe2O3 and Cr2O3 to CrO3.
Nano particles of Fe3O4 are used as contrast agents in MRI scanning.
Ferumoxytol, also known as Feraheme and Rienso, is an intravenous Fe3O4 preparation for treatment of anemia resulting from chronic kidney disease. Ferumoxytol is manufactured and globally distributed by AMAG Pharmaceuticals. Along with sulfur and aluminium, it is an ingredient in a specific type of thermite useful for cutting steel.
Bluing is a passivation process that produces a layer of Fe3O4 on the surface of steel to protect it from rust.