Mineral Information and Data:

Birnessite
(Na,Ca,K)0.6(Mn4+,Mn3+)2O4 • 1.5H2O [CNMNC approved formula]

Named after the locality : Birness, Aberdeenshire, Scotland.

IMA status : Valid species (Pre-IMA 1956) Grandfathered
CLASSIFICATION 
Dana
(8th edition) :
07.05.03.01  
  (07) Multiple Oxides
  (07.05) where A B X2
  (07.05.03)
  
Nickel-Strunz
(10th edition) :
04.FL.45
  (04) Oxides and Hydroxides
  (04.F) Hydroxides (without V or U)
  (04.FL) Hydroxides with H2O +- (OH); sheets of edge-sharing octahedra
  
Crystal system: Monoclinic System
Point group (H-M): 2/m — prismatic
Space group: C2/m
Unit cell: a = 5.175(1)Å, b = 2.850(1)Å, c = 7.337(3)Å, β = 103.18(2)°, Z=1
Crystal Habit: Rarely in platelets, to 50 μm; commonly extremely finely crystalline, spherulitic, cellular.
  
Color: Black; dark brown in transmitted light
Diaphaneity: Nearly opaque
Luster: Dull
Hardness (Mohs): 1.5
Measured Density: 3.0 g/cm3
  
Geologic Setting: A major manganese-bearing mineral of many soils; a common alteration product of manganese-rich mineral deposits; a component of bacterially-precipitated manganese oxides; an important constituent of “desert varnish” and marine manganese nodules.
Mineral Association: Rhodonite, rhodochrosite, tephroite, spessartine, alleghanyite, cummingtonite (Cummington, Massachusetts, USA); manganese and iron oxides, calcium carbonate (marine nodules)
  
Other Properties: BioMineral.

 

Birnessite
Birnessite on calcite, 2.7 x
Origin: U.S. Borax Open Pit, Boron, Kern Co., California
Microscopic image, about 1 cm
Photo and owner: Milton Speckels

 

Birnessite
Birnessite on colemanite, 3.2 x
Origin: U.S. Borax Open Pit, Boron, Kern Co., California
Microscopic image, about 1 cm
Photo and owner: Milton Speckels

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