Mineral Information and Data:

Armangite
Mn2+26As3+18O50(CO3)(OH)4 [CNMNC approved formula]

Named for Arsenic and MANGanese in the composition.

IMA status : Valid species (Pre-IMA 1920) Grandfathered
CLASSIFICATION 
Dana
(8th edition) :
46.02.07.01  
  (46) Basic or Halogen-Containing Antimonites, Arsenites and Phosphites
  (46.02) with miscellaneous formulae
  (46.02.07)
  
Nickel-Strunz
(10th edition) :
04.JB.20
  (04) Oxides and Hydroxides
  (04.J) Arsenites, Antimonites, Bismuthites, Sulfites,
  (04.JB) Arsenites, antimonites, bismuthites; with additional anions, without H2O
  
Crystal system: Trigonal System
Point group (H-M): 3 — rhombohedral
Unit cell: a = 13.491 Å, c = 8.855 Å
Crystal Habit: Crystals short prismatic; lamellar
Twinning: on {1120}
  
Color: Black to pale brown
Diaphaneity: Opaque, transparent in splinters
Hardness (Mohs): 4
Measured Density: 4.43 g/cm3
Cleavage: 1; {0001}fair to poor
Streak: Brown
  
Geologic Setting: On a museum specimen collected from a metamorphosed Fe–Mn deposit.
Mineral Association: Calcite, dolomite, barite, hematite, fluorite, manganarsite, hausmannite.
  

 

Armangite
partial crystals of the very rare mineral armangite on calcite and barite. It also has ecdemite present as amorphous smears of olive green colored mineral.
Origin: Långban, Sweden
Sample size: 4 x 3.7 x 2 cm
Photo: John Veevaert, Trinity Mineral Co

 

Armangite
(zoom-in of above)

 

Armangite
(zoom-in of above)

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