Manganite

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This article is about the mineral of formula MnO(OH), for other uses of the term manganite see Manganite (disambiguation)
Manganite
Manganite-180085.jpg
Manganite, Ilfeld, Thuringia, Germany (size: 5.2×4.1×2.7 cm)
General
Category Oxide mineral
Formula
(repeating unit)
MnO(OH)
Strunz classification 04.FD.15
Dana classification 06.01.03.01
Crystal symmetry Monoclinic 2/m prismatic
Unit cell a = 8.94 Å, b = 5.28 Å, c = 5.74 Å; β = 90°; Z = 8
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
Crystal system Monoclinic, pseudo-orthorhombic
Twinning Contact and penetration twins on {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 [1][2][3][4][5]

Manganite is a mineral. Its composition is manganese oxide-hydroxide, MnO(OH), crystallizing in the monoclinic system (pseudo-orthorhombic).[1] 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.

Occurrence[edit]

Manganite crystal group

Manganite occurs with other manganese oxides in deposits formed by circulating meteoric water in the weathering environment in clay deposits and laterites. It forms by low temperature hydrothermal action in veins in association with calcite, barite, and siderite. Often associated with pyrolusite, braunite, hausmannite and goethite.[1][4]

Manganite occurs in specimens exhibiting good crystal form at Ilfeld in the Harz Mountains of Germany,[5] where the mineral occurs with calcite and barite in veins traversing porphyry. Crystals have also been found at Ilmenau in Thuringia, Neukirch near Sélestat in Alsace (newkirkite), Granam near Towie in Aberdeenshire, and in Upton Pyne near Exeter, UK and Negaunee, Michigan, United States, and in the Pilbarra of Western Australia. Good crystals have also been found at Atikokan, Ontario and Nova Scotia, Canada. As an ore of manganese it is much less abundant than pyrolusite or psilomelane.

Although described with various other names as early as 1772, the name manganite was first applied in a publication by W. Haidinger in 1827.[6]

Crystal structure of manganite

See also[edit]

References[edit]

  1. ^ a b c Handbook of Mineralogy
  2. ^ Mindat
  3. ^ Webmineral data
  4. ^ a b Klein, Cornelis and Cornelius S. Hurbut, Jr., Manual of Mineralogy, Wiley, 20th ed., 1985, p. 317 ISBN 0-471-80580-7
  5. ^ a b T. P. Moore, Famous Mineral Localities: Ilfeld, Harz Mountains, Thuringia, Germany, The Mineralogical Record, vol. 41, no. 6, 2010.
  6. ^ Palache, Charles, Harry Berman and Clifford Frondel, The System of Mineralogy V.1, p. 646, Wiley, 7th ed., 1944