Hausmannite
General
Category	Oxide mineral
Formula (repeating unit)	MnIIMnIII2O4, MnO·Mn2O3, or Mn3O4
IMA symbol	Hsm[1]
Strunz classification	4.BB.10
Crystal system	Tetragonal
Crystal class	Ditetragonal dipyramidal (4/mmm) H-M symbol: (4/m 2/m 2/m)
Space group	I41/amd
Unit cell	a = 5.76 Å c = 9.46 Å; Z = 4
Identification
Formula mass	228.81 g/mol
Color	Brownish black, grayish.
Crystal 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 scale hardness	5.5
Luster	Submetallic
Streak	Dark reddish brown
Diaphaneity	Opaque, transparent on thin edges
Specific gravity	4.7 – 4.84, average = 4.76
Optical properties	Uniaxial (−)
Refractive index	nε = 2.15, nω = 2.46
Birefringence	δ = 0.31
Other characteristics	Anisotropism: Distinct, bireflectance: weak; O = light gray; E = dark gray.
References	[2][3][4]

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 Mn^IIMn^III₂O₄, or more simply noted as MnO·Mn₂O₃, or Mn₃O₄, as commonly done for magnetite (Fe₃O₄), 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.^[3] Locations include Batesville, Arkansas, US; Ilfeld, Germany; Langban, Sweden; and the Ural Mountains, Russia.^[2] 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.^[3]

Image gallery

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  Hausmannite from Wessels mine, Kalahari manganese fields, Northern Cape Province, South Africa
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  Crystal structure of hausmannite
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  Cluster from Wessels mine, Hotazel, Kalahari manganese fields, Northern Cape Province, South Africa
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  Ettringite crystal on a matrix of hausmannite and hematite, coated by oyelite