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Manganite

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Manganite is a member of oxide minerals with composed of manganese oxide-hydroxide of formula: MnO(OH).A widespread and important ore of manganese. The mineral had been described by a number of different names since 1772, but was finally given its current name, which it owes to its manganese component, in 1827. Opaque and metallic dark gray or black, crystals of manganite are mostly pseudoorthorhombic prisms, typically with flat or blunt terminations, and are often grouped in bundles and striated lengthwise. Multiple twinning is common. Manganite can also be massive or granular; it is then hard to distinguish by eye from other manganese oxides, such as pyrolusite. An important ore of manganese, manganite occurs in hydrothermal deposits formed at low temperature (up to 400°F/200°C) with calcite, siderite, and barite, and in replacement deposits with goethite. Manganite also occurs in hot-spring manganese deposits. It alters to pyrolusite and may form by the alteration of other manganese minerals.

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

Name: For MANGANese in the composition.

Association: Pyrolusite, braunite, hausmannite, barite, calcite, siderite, goethite.

Polymorphism & Series: Trimorphous with feitknechtite and groutite

Environment: In low temperature hydrothermal replacement deposits, acid-rich bogs, and in manganese-rich hot springs.

Composition: MnO(OH). Mn = 62.4 per cent, 0 = 27.3 percent, H20 = 10.3 percent.

Diagnostic Features: Told chiefly by its black color, prismatic crystals, hardness (4), and brown streak. The last two will serve to distinguish it from pyrolusite.

Crystallography: Orthorhombic; dipyramidal. Crystals usually long prismatic with obtuse terminations, deeply striated vertically. Often twinned. Crystals often grouped in bundles or in radiating masses; also columnar.

Chemical Properties

Chemical Classification Oxide mineral
Formula MnO(OH)
Common Impurities Fe,Ba,Pb,Cu,Al,Ca

Manganite Physical Properties

Crystal habit Slender prismatic crystals, massive to fibrous, pseudo-orthorhombic
Color Gray-black, black
Streak Reddish brown to black
Luster Resinous, Sub-Metallic, Dull
Cleavage Perfect {010} perfect; {110} and {001} good.
Diaphaneity Opaque
Mohs Hardness 4
Crystal System Monoclinic
Tenacity Brittle
Density 4.29 – 4.34 g/cm3 (Measured)    4.38 g/cm3 (Calculated)
Fracture Splintery

Manganite Optical Properties

Type Anisotropic
Anisotropism Weak
Color / Pleochroism Weak
2V: Small
RI values: nα = 2.250(2) nβ = 2.250(2) nγ = 2.530(2)
Twinning Contact and penetration Twins on {011}; lamellar on {100}.
Optic Sign Biaxial (+)
Birefringence 0.028
Relief Very High
Dispersion: r > v extreme

Occurrence

Formed in low-temperature hydrothermal or hot-spring manganese deposits; replacing other manganese minerals in sedimentary deposits; a component in some clay deposits and laterites.

Manganite is found associated with other manganese oxides and has a similar origin. It frequently alters to pyrolusite. Found often in veins associated with the granitic igneous rocks, both filling cavities and as a replacement of the neighboring rocks. Barite and calcitc are frequent associates.

Manganite Uses Area

  • A minor ore of manganese.
  • In mineral prehistoric times, a pigment has been used by humans and as the igniter of Neanderthals. Manganite is believed to be used in prehistoric times to burn wood fire. Manganite reduces the combustion temperature of the wood from 350 degrees Celsius to 250 degrees Celsius. Manganite dust is a common finding in Neanderthal archaeological sites.

Distribution

Many localities, but rarely well-crystallized.

  • Fine crystals from Ilfeld, Harz Mountains, and Ilmenau, Thuringia, Germany.
  • In the Botallack mine, St. Just, Cornwall; from Egremont, Cumbria; and at Upton Pyne, Exeter, Devonshire, England.
  • From Granam, near Towie, Aberdeenshire, Scotland.
  • At Bolet, near Karlsborg, Vastergotland,Sweden.
  • In the USA, good crystals from the Negaunee and Marquette districts, Marquette Co., Michigan; in the Powell’s Fort mine, near Woodstock, Shenandoah Co., Virginia; and at Lake Valley, Sierra Co., New Mexico.
  • From the Caland mine, Atikokan, Ontario, Canada.
  • At Kuruman, Cape Province, South Africa.

References

  • Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
  • Dana, J. D. (1864). Manual of Mineralogy… Wiley.
  • Handbook of Mineralogy. [online] Available at: http://www.handbookofmineralogy.org [Accessed 4 Mar. 2019].
  • Mineral information, data and localities.. [online] Available at: https://www.mindat.org/ [Accessed. 2019].
Cite this article as: Geology Science. (2019). Manganite. [online] Available at: http://geologyscience.com/minerals/manganite/ [14th December 2019 ]
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