Manganite
Manganite is a mineral composed of manganese oxide-hydroxide, MnO(OH), crystallizing in the monoclinic system (pseudo-orthorhombic). 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.
| Manganite | |
|---|---|
| General | |
| Category | Oxide mineral |
| Formula (repeating unit) | MnO(OH) |
| IMA symbol | Mnn |
| 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 | |
The mineral contains 89.7% manganese sesquioxide; it dissolves in hydrochloric acid with evolution of chlorine.
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