Birnessite - Occurrence, Properties, and Distribution

Birnessite is an oxide mineral of manganese along with sodium, potassium and calcium. The mineral was first described in 1956 from the Birness, Aberdeenshire, Scotland. It was named after the place of discovery.

Properties of Birnessite

The following are the key properties of Birnessite:

  • Cell Data
    • Space Group: C2/m (synthetic ∼Na0.58 (Mn4+1.42Mn3+0.58)Σ=2.00O4 •1.5H2O)
    • a = 5.175(1)
    • b = 2.850(1)
    • c = 7.337(3)
    • β = 103.18(2)°
    • Z = 1.
  • Crystal Data
    • Monoclinic, pseudohexagonal
    • Point Group: 2/m
    • Rarely in platelets, to 50 µm; commonly extremely finely crystalline, spherulitic, cellular
    • X-ray Powder Pattern: 7.08 (100), 2.333 (43), 1.711 (29), 3.547 (28), 2.031 (24), 2.468 (17), 1.426 (17).
  • Chemical Composition
Elements Content 1 Content 2
MnO2 75.8 61.4
H2O 10.89 12.72
MgO 6.2 -
Na2O 1.9 7.3
K2O 1.8 -
SiO2 0.9 -
NiO 0.8 -
FeO 0.55 -
CaO 0.39 -
CuO 0.33 -
S 0.2 -
CoO 0.14 -
Cl 0.1 -
Total 100 100
  • Optical Properties
    • Optical Class: Pseudouniaxial (–); identification by optical properties is impossible
    • ω = ∼1.73
    • ε = ∼1.69.
  • Estimated Properties
Electron density Bulk density (electron density) = 2.9 g/cm3
note: Specific gravity of Birnessite = 3 g/cm3
Photoelectric PEBirnessite = 13.58 barns/electron
U = PEBirnessite x ρ Electron density = 39.35 barns/cm3
Fermion index Fermion index = 0.0002
Boson index = 0.99
Radioactivity

Birnessite is barely detectable.

How to Identify Birnessite

Birnessite is a dark brown or black mineral having sub-metallic luster and sub-opaque appearance. It can be formed as earthy, dull crystals or massive uniformly undistinguishable crystals. The density of birnessite is 3 g/cm3, and its hardness is 1.5.

Global Distribution

Birnessite is distributed in the following places:

  • Birness, Aberdeenshire, Scotland
  • Treburland mine, Altarnun, and the Penberthy Croft mine, St. Hilary, Cornwall, England
  • Groote Eylandt, Northern Territory, and near Noarlunga, Mount Lofty Ranges, South Australia
  • Ioi mine, Ritta, Shiga Prefecture, Japan
  • Sterling Hill, Sussex Co., New Jersey, USA
  • Cummington, Hampshire Co., Massachusetts
  • Kramer borate deposit, Boron, Kern Co., California
  • Silver Cliff, Custer Co., Colorado
  • Mont St. Hilaire, Quebec, Canada.

Occurrence of Birnessite and Useful Mineral Association

Birnessite occurs as a major manganese-bearing mineral of many soils; a common alteration product of manganese-rich mineral deposits; a component of bacterially-precipitated manganese oxides. It can also be formed as an important constituent of “desert varnish” and marine manganese nodules. It is closely associated with calcium carbonate, manganese and iron oxides, cummingtonite, alleghanyite, spessartine, tephroite, rhodochrosite and rhodonite.

References

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