From HandWiki
Short description
Manganese hydroxide mineral
Birnessite 01.jpg
CategoryOxide mineral
(repeating unit)
Strunz classification4.FL.45
Dana classification07.05.03.01
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupC2/m
ColorDark brown to black
Crystal habitRarely in platelets, to 50 μm; commonly extremely finely crystalline, spherulitic, cellular (pseudohexagonal).
Cleavage[001] perfect
Mohs scale hardness1.5
|re|er}}Sub-metallic, dull
DiaphaneityNearly opaque
Specific gravity3.0
Optical propertiesUniaxial (-)
Refractive indexnω = 1.730 nε = 1.690
Birefringenceδ = 0.040
Other characteristicsIdentification by optical properties is impossible.

Birnessite (Na0.3Ca0.1K0.1)(Mn4+,Mn3+)2O4 · 1.5 H2O is an oxide mineral of manganese along with calcium, potassium and sodium. It has a dark brown to black color with a submetallic luster. It is also very soft, with a Mohs hardness of 1.5. Birnessite is formed by precipitation in lakes, oceans and groundwater and is a major component of desert varnish and deep sea manganese nodules.


It was first described in 1956 and named for an occurrence in Birness, Aberdeenshire, Scotland. Birnessite is found as an oxidation product of several other minerals, including rhodonite, rhodochrosite, and as a weathering product of franklinite-willemite ore. It has also been found as a coating along joint planes and fractures within a trachyte sill. However, it has been most commonly seen as a constituent of oceanic nodules of manganese.

A recent study found that the mineral is able to break down prions via oxidation. How well this process works outside the laboratory is unclear.[4]

Geologic occurrence

Levinson[5] noted the presence of Birnessite in one or more mines from the region around Zacatecas, Mexico, while other notations have been made in Canada , at Cummington, Massachusetts , from the aforementioned nodules in both the Atlantic and Pacific Oceans, from the Tachaki Mine in Japan , the Treburland Mine in Cornwall, England , and from a bog in Norway .[6]

Composition and structure

Birnessite is a phyllomanganate, which is a type of hydrated metal oxide that contains a high proportion of manganese. While natural forms generally contain foreign ions (i.e. Na, Ca, K) they are considered non-essential and synthetic forms of the mineral can be produced without them. However, most of the synthetic versions of the mineral undergo significant water loss at temperatures above 100 °C. Its structure is thought to be similar to that of chalcophanite,[7] and has been modeled as such by Burns.[8] The structure itself consists of sheets of water molecules found between sheets of edge-sharing molecules of MnO6 octahedra, and repeated on an average of every 7.2 Å, doing so along the c-axis. Of the six octahedral sites in the MnO6 octahedral layer, one is left unoccupied; Mn2+ and Mn3+ lie above each vacant slot on the octahedral. These Mn ions are low-valence, and associate with O, in both the octahedral and in the water sheets.[9]

Properties and application

Research results published in 2015 show that 2.50 eV band gap of birnessite could be used to harvest sunlight to split water into hydrogen and oxygen.[10]

See also

Other manganese oxides:


  1. Handbook of Mineralogy
  2. Mindat with location data
  3. Webmineral data
  4. Common Soil Mineral Degrades The Nearly Indestructible Prion
  5. Levinson, A.A. (1962) Mineralogical Notes,. The American Mineralogist Vol 47, May–June, (1962)[1]
  6. Nicholson, K. (1988) Mineralogical Notes. Mineralogical Magazine, June (1988) Vol. 2 p. 415-417 [2]
  7. Holland K.L., and Walker, J.R. Crystal structure modeling of a highly disordered potassium birnessite. Clays and Clay Minerals. (1996) 44, 61, 744-748 [3]
  8. [4]
  9. Johnson, E.A., Post, J.E. Water in the interlayer region of birnessite: Importance in cation exchange and structural stability. American Mineralogist April (2006), v. 91 no.4 p. 609-618.[5]
  10. Lucht, Kevin P.; Mendoza-Cortes, Jose L. (8 October 2015). "Birnessite: A layered manganese oxide to capture sunlight for water-splitting catalysis". The Journal of Physical Chemistry C 119 (40): 22838–22846. doi:10.1021/acs.jpcc.5b07860.