Magnetite is the most extensively studied magnetic mineral. It is a cubic inverse spinel that occurs commonly in most rock types and is also produced by organisms. Its fundamental magnetic parameters are well known, which has enabled development of a micromagnetic framework for magnetic domain state variations with respect to particle size and shape, which complements an extensive experimental magnetic property framework. When cooling through the Verwey transition at 120 K, its structure changes from cubic to monoclinic. It also has an isotropic point where the first and second anisotropy constants change from negative above to positive below 130 K. Shape anisotropy dominates cubic magnetocrystalline anisotropy for elongated particles, which produces wider size ranges for the stable single domain state with elongation. The magnetite formation mode controls its magnetic properties because of its sensitivity to internal strain. Its magnetic susceptibility does not vary with particle size, while other laboratory-imparted remanences vary with particle size. These properties are useful for magnetic granulometry. Magnetite is a low coercivity mineral with Curie temperature of 580°C.