Mineral Information and Data:

Mn2+O [CNMNC approved formula]

Named from its composition.

IMA status : Valid species (Pre-IMA 1874) Grandfathered
(8th edition) :  
  (04) Simple Oxides
  (04.02) with a cation charge of 2+ (A++ O)
  (04.02.01) Periclase group (Isometric, Fm3m)
(10th edition) :
  (04) Oxides and Hydroxides
  (04.A) Metal:Oxygen = 2.1 and 1:1
  (04.AB) M:O = 1:1 (and up to 1:1.25); with small to medium-sized cations only
Crystal system: Cubic System
Point group (H-M): m3m (or 4/m 3 2/m) — hexoctahedral
Unit cell: a = 4.44 Å
Crystal Habit: Crystals octahedral; massive; irregular grains
Color: Emerald green; becomes black on exposure
Diaphaneity: Transparent
Luster: Vitreous
Hardness (Mohs): 5.5
Measured Density: 5.364 g/cm3
Cleavage: 1; {001} fair
Tenacity: No data
Fracture: Fibrous
Streak: Brown
Geologic Setting: An alteration product of rhodochrosite or other manganese minerals, formed during oxygen-deficient metamorphism of manganese-bearing deposits; in marine manganese nodules.
Mineral Association: Pyrochroite, manganite, dolomite (L°angban, Sweden); pyrochroite, hausmannite, garnet, dolomite (Nordmark, Sweden); franklinite, willemite, zincite (Franklin, New Jersey, USA)


This cabinet specimen has very large crystallized grains in excess of 1 cm - actually up to 1.3 cm across! This is larger than the book on Långban reported being found. Manganosite is a simple oxide of manganese which is deep green on fresh surfaces and then tend to alter to manganite, pyrochroite or some other form of manganese oxide. This specimen has matrix comprised of calcite which fluoresces under SW UV light. Though not a rare species at Långban the size of the grains is quite exceptional.
Origin: Långban, Sweden
Sample size: 8.5 x 7.5 x 4.2 cm
Photo: John Veevaert, Trinity Mineral Co


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Black manganosite crystals in pink sonolite with foliated zincite.
Origin: Franklin Mine, Sussex County, New Jersey, U.S.A.
Sample size: 10 x 6 x 4.5 cm
Photo: Rob Lavinsky


(zoom-in of above)