Birnessite

Birnessite
General
Category	Oxide mineral
Formula; (repeating unit)	(Na0.3Ca0.1K0.1)(Mn4+,Mn3+)2O4·1.5H2O
Strunz classification	4.FL.45
Dana classification	07.05.03.01
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) ; (same H-M symbol)
Space group	C2/m
Identification
Color	Dark brown to black
Crystal habit	Rarely in platelets, to 50 μm; commonly extremely finely crystalline, spherulitic, cellular (pseudohexagonal).
Cleavage	[001] perfect
Mohs scale hardness	1.5
Luster	Sub-metallic, dull
Diaphaneity	Nearly opaque
Specific gravity	3.0
Optical properties	Uniaxial (-)
Refractive index	nω = 1.730 nε = 1.690
Birefringence	δ = 0.040
Other characteristics	Identification by optical properties is impossible.
References	[1][2][3]

Birnessite (Na_0.3Ca_0.1K_0.1)(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.

History

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 2.50eV band gap of Birnessite could be used to harvest sunlight to split water into hydrogen and oxygen.[10]

References

http://www.handbookofmineralogy.org/pdfs/birnessite.pdf Handbook of Mineralogy
http://www.mindat.org/min-680.html Mindat with location data
http://www.webmineral.com/data/Birnessite.shtml Webmineral data
https://www.sciencedaily.com/releases/2009/01/090114142028.htm Common Soil Mineral Degrades The Nearly Indestructible Prion
Levinson, A.A. (1962) Mineralogical Notes,. The American Mineralogist Vol 47, May–June, (1962)
Nicholson, K. (1988) Mineralogical Notes. Mineralogical Magazine, June (1988) Vol. 2 p. 415-417
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
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.
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.

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[1] ttp://www.handbookofmineralogy.org/pdfs/birnessite.pdf Handbook of Mineralogy

[2] ttp://www.mindat.org/min-680.html Mindat with location data

[3] ttp://www.webmineral.com/data/Birnessite.shtml Webmineral data

[4] ttps://www.sciencedaily.com/releases/2009/01/090114142028.htm Common Soil Mineral Degrades The Nearly Indestructible Prion

[5] Levinson, A.A. (1962) Mineralogical Notes,. The American Mineralogist Vol 47, May–June, (1962)

[6] Nicholson, K. (1988) Mineralogical Notes. Mineralogical Magazine, June (1988) Vol. 2 p. 415-417

[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

[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.

[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.