hausmannite

{{Infobox mineral | name = Hausmannite | category = Oxide mineral | image = Hausmannite-215565.jpg | imagesize = 260px | caption = | formula = {{chem2|Mn^{II}Mn^{III}2O4}},, or | IMAsymbol = Hsm | molweight = 228.81 g/mol | strunz = 4.BB.10 | system = Tetragonal | class = Ditetragonal dipyramidal (4/mmm) H-M symbol: (4/m 2/m 2/m) | symmetry = I41/amd | unit cell = a = 5.76 Å c = 9.46 Å; Z = 4 | color = Brownish black, grayish. | habit = Massive – granular – common texture observed in granite and other igneous rock. pseudo octahedral – crystals show an octahedral outline. | twinning = Repeated twins on {112} | cleavage = [001] Perfect | fracture = Uneven – flat surfaces (not cleavage) fractured in an uneven pattern. | tenacity = Brittle | mohs = 5.5 | luster = Submetallic | refractive = nε = 2.15, nω = 2.46 | opticalprop = Uniaxial (−) | birefringence = δ = 0.31 | pleochroism = | streak = Dark reddish brown | gravity = 4.7 – 4.84, average = 4.76 | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Opaque, transparent on thin edges | other = Anisotropism: Distinct, bireflectance: weak; O = light gray; E = dark gray. | references = }} Hausmannite is a complex oxide, or a mixed oxide, of manganese containing both di- and tri-valent manganese. Its chemical formula can be represented as {{chem2|Mn^{II}Mn^{III}2O4}}, or more simply noted as , or , as commonly done for magnetite (), the corresponding iron oxide. It belongs to the spinel group and forms tetragonal crystals. Hausmannite is a brown to black metallic mineral with Mohs hardness of 5.5 and a specific gravity of 4.8.

The type locality is Oehrenstock (Öhrenstock), Ilmenau, Thuringian Forest, Thuringia, Germany, where it was first described in 1813. Locations include Batesville, Arkansas, US; Ilfeld, Germany; Langban, Sweden; and the Ural Mountains, Russia. High quality samples have been found in South Africa and Namibia where it is associated with other manganese oxides, pyrolusite and psilomelane and the iron-manganese mineral bixbyite. Wilhelm Haidinger (1827) named it in honour of Johann Friedrich Ludwig Hausmann (1782–1859), Professor of Mineralogy, University of Göttingen, Germany.