Hausmannite

Hausmannite
Hausmannite sample from the collection of the National Museum, Prague, Czech Republic
General
Category	Oxide mineral
Formula (repeating unit)	Mn2+Mn3+2O4
Strunz classification	04.BB.10
Crystal system	Tetragonal
Space group	Tetragonal - ditetragonal dipyramidal H-M symbol: (4/m 2/m 2/m) Space group: I 41/amd
Unit cell	a = 5.76 Å, c = 9.46 Å; Z=4
Identification
Formula mass	228.81
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

Hausmannite is a complex oxide of manganese containing both di- and tri-valent manganese. The formula can be represented as Mn²⁺Mn³⁺₂O₄. 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.

References

Crystal structure of hausmannite

Hausmannite from Wessels Mine, Kalahari manganese fields, Northern Cape Province, South Africa (size: 5.8 x 4.3 x 3.5 cm)