Mineral Information and Data:

Manganite
Mn3+O(OH) [CNMNC approved formula]

Named for MANGANese in the composition. Called the prismatoidal manganese ore in 1826.

IMA status : Valid species (Pre-IMA 1828) Grandfathered
CLASSIFICATION 
Dana
(8th edition) :
06.01.03.01  
  (06) Hydroxides and Oxides Containing Hydroxyl
  (06.01) where X+++O OH
  (06.01.03)
  
Nickel-Strunz
(10th edition) :
04.FD.15
  (04) Oxides and Hydroxides
  (04.F) Hydroxides (without V or U)
  (04.FD) Hydroxides with OH, without H2O; chains of edge-sharing octahedra
  
Crystal system: Monoclinic System
Point group (H-M): 2/m — prismatic
Space group: B21/d
Unit cell: a = 8.94Å, b = 5.28Å, c = 5.74Å, β = 90°, Z=8
Crystal Habit: Crystals prismatic and striated || [001], short to long, to 7.5 cm; typically terminated by {001}, {h0l}, may be complex. In bundles, subparallel [001], fibrous; granular, massive.
Twinning: Contact and penetration twins on {011}; lamellar on {100}
  
Color: Dark steel-gray to iron-black; red-brown in transmitted light; in reflected light, gray-white with brownish tint, with blood-red internal reflections
Diaphaneity: Opaque, transparent on thin edges
Luster: Submetallic
Hardness (Mohs): 4
Measured Density: 4.29 – 4.34 g/cm3
Cleavage: {010}, perfect; {110} and {001}, good
Tenacity: Brittle
Fracture: Uneven
Streak: Reddish brown to nearly black
  
Polymorphism and Series: Trimorphous with feitknechtite and groutite.
Geologic Setting: 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.
Mineral Association: Pyrolusite, braunite, hausmannite, barite, calcite, siderite, goethite
  

 

Manganite
Origin: Ilfeld, Harz Mtns., Germany
Sample size: 4.5 x 4 x 3.5 cm
Photo: Rob Lavinsky

 

Manganite
(zoom-in of above)

 

Manganite
Twinned manganite.
Origin: Ilfeld, nr. Nordhausen, Thuringa, Germany (type locality)
Sample size: 5.7 x 5 x 3.8 cm
Photo: John Veevaert, Trinity Mineral Co.

 

Manganite
(zoom-in of above) showing details of twinning.

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