Manganite

Manganite
Manganite, Ilfeld, Thuringia, Germany (size: 5.2×4.1×2.7 cm)
General
Category	Oxide mineral
Formula (repeating unit)	MnO(OH)
IMA symbol	Mnn[1]
Strunz classification	4.FD.15
Dana classification	06.01.03.01
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	P21/c
Unit cell	a = 5.3 Å, b = 5.278 Å, c = 5.307 Å; β = 114.36°; Z = 4
Identification
Color	Dark steel-gray to black, reddish brown in transmitted light, gray-white with brownish tint, with blood-red internal reflections in reflected light
Crystal habit	Slender prismatic crystals, massive to fibrous, pseudo-orthorhombic
Twinning	{011}
Cleavage	{010} perfect, {110} and {001} good
Fracture	Uneven
Tenacity	Brittle
Mohs scale hardness	4
Luster	Sub-metallic
Streak	Reddish brown to nearly black
Diaphaneity	Opaque, transparent on thin edges
Specific gravity	4.29–4.34
Optical properties	Biaxial (+)
Refractive index	nα = 2.250(2) nβ = 2.250(2) nγ = 2.530(2)
Birefringence	δ = 0.280, Bireflectance: distinct in grays
Pleochroism	Faint
2V angle	Small
Dispersion	Very strong
References	[2][3][4][5][6][7]

Manganite is a mineral composed of manganese oxide-hydroxide, MnO(OH), crystallizing in the monoclinic system (pseudo-orthorhombic).^[3] Crystals of manganite are prismatic and deeply striated parallel to their length; they are often grouped together in bundles. The color is dark steel-grey to iron-black, and the luster brilliant and submetallic. The streak is dark reddish brown. The hardness is 4, and the specific gravity is 4.3. There is a perfect cleavage parallel to the brachypinacoid, and less-perfect cleavage parallel to the prism faces. Twinned crystals are not infrequent.

The mineral contains 89.7% manganese sesquioxide; it dissolves in hydrochloric acid with evolution of chlorine.