Birnessite: Difference between revisions

| opticalprop = Uniaxial (-−)

'''Birnessite''' (nominally MnO₂·''n''H₂O), also known as δ-{{chem2|MnO2}}, is a hydrous manganese dioxide [[mineral]] with a chemical formula of Na_0.7Ca_0.3Mn₇O₁₄·2.8H₂O.<ref>{{Cite journal|last1=Jones|first1=L. H. P.|display-authors=1|last2=Milne|first2=Angela A.|date=1956|title=Birnessite, a new manganese oxide mineral from Aberdeenshire, Scotland|url=http://dx.doi.org/10.1180/minmag.1956.031.235.01|journal=Mineralogical Magazine and Journal of the Mineralogical Society|volume=31|issue=235|pages=283–288|doi=10.1180/minmag.1956.031.235.01|bibcode=1956MinM...31..283J}}</ref> It is the main [[manganese]] [[mineral]] species at the Earth's surface, and commonly occurs as fine-grained, poorly crystallized aggregates in [[soil]]s, [[sediment]]s, grain and rock coatings (e.g., [[desert varnish]]), and marine [[ferromanganese nodules]] and crusts.<ref>{{Cite journal|last1=McKeown|first1=D. A.|display-authors=1|last2=Post|first2=Jeffrey E.|date=2001-05-01|title=Characterization of manganese oxide mineralogy in rock varnish and dendrites using X-ray absorption spectroscopy|url=https://www.degruyter.com/document/doi/10.2138/am-2001-5-611/html|journal=American Mineralogist|language=en|volume=86|issue=5–6|pages=701–713|doi=10.2138/am-2001-5-611|bibcode=2001AmMin..86..701M|s2cid=19647389}}</ref><ref>{{Cite journal|last1=[[Alain Manceau|Manceau]]|first1=A|display-authors=1|last2=Tamura|first2=Nobumichi|last3=Celestre|first3=Richard S.|last4=MacDowell|first4=Alastair A.|last5=Geoffroy|first5=Nicolas|last6=Sposito|first6=Garrison|last7=Padmore|first7=Howard A.|date=2003|title=Molecular-Scale Speciation of Zn and Ni in Soil Ferromanganese Nodules from Loess Soils of the Mississippi Basin|url=https://pubs.acs.org/doi/10.1021/es025748r|journal=Environmental Science & Technology|language=en|volume=37|issue=1|pages=75–80|doi=10.1021/es025748r|pmid=12542293|bibcode=2003EnST...37...75M}}</ref><ref name=":0">{{Cite journal|last1=Isaure|first1=M-P|display-authors=1|last2=[[Alain Manceau|Manceau]]|first2=A|last3=Geoffroy|first3=Nicolas|last4=Laboudigue|first4=Agnès|last5=Tamura|first5=Nobumichi|last6=Marcus|first6=M. A.|date=2005|title=Zinc mobility and speciation in soil covered by contaminated dredged sediment using micrometer-scale and bulk-averaging X-ray fluorescence, absorption and diffraction techniques|url=https://linkinghub.elsevier.com/retrieve/pii/S0016703704006519|journal=Geochimica et Cosmochimica Acta|language=en|volume=69|issue=5|pages=1173–1198|doi=10.1016/j.gca.2004.08.024|bibcode=2005GeCoA..69.1173I}}</ref><ref name=":1">{{Cite journal|last1=[[Alain Manceau|Manceau]]|first1=A|display-authors=1|last2=Lanson|first2=Martine|last3=Geoffroy|first3=Nicolas|date=2007|title=Natural speciation of Ni, Zn, Ba, and As in ferromanganese coatings on quartz using X-ray fluorescence, absorption, and diffraction|url=https://linkinghub.elsevier.com/retrieve/pii/S0016703706020205|journal=Geochimica et Cosmochimica Acta|language=en|volume=71|issue=1|pages=95–128|doi=10.1016/j.gca.2006.08.036|bibcode=2007GeCoA..71...95M}}</ref><ref>{{Cite journal|last1=[[Alain Manceau|Manceau]]|first1=A.|display-authors=1|last2=Lanson|first2=M.|last3=Takahashi|first3=Y.|date=2014|title=Mineralogy and crystal chemistry of Mn, Fe, Co, Ni, and Cu in a deep-sea Pacific polymetallic nodule|url=https://www.degruyter.com/document/doi/10.2138/am-2014-4742/html|journal=American Mineralogist|language=en|volume=99|issue=10|pages=2068–2083|doi=10.2138/am-2014-4742|bibcode=2014AmMin..99.2068M|s2cid=98025822}}</ref><ref>{{Cite journal|last1=Bodeï|first1=S.|display-authors=1|last2=[[Alain Manceau|Manceau]]|first2=A|last3=Geoffroy|first3=Nicolas|last4=Baronnet|first4=A|last5=Buatier|first5=Martine|date=2007|title=Formation of todorokite from vernadite in Ni-rich hemipelagic sediments|url=https://linkinghub.elsevier.com/retrieve/pii/S0016703707004358|journal=Geochimica et Cosmochimica Acta|language=en|volume=71|issue=23|pages=5698–5716|doi=10.1016/j.gca.2007.07.020|bibcode=2007GeCoA..71.5698B}}</ref><ref>{{Cite journal|last1=Bargar|first1=J.R.|display-authors=1|last2=Fuller|first2=Christopher C.|last3=Marcus|first3=M. A.|last4=Brearley|first4=Adrian J.|last5=Perez De la Rosa|first5=M.|last6=Webb|first6=Samuel M.|last7=Caldwell|first7=Wendel A.|date=2009|title=Structural characterization of terrestrial microbial Mn oxides from Pinal Creek, AZ|url=https://linkinghub.elsevier.com/retrieve/pii/S0016703708006777|journal=Geochimica et Cosmochimica Acta|language=en|volume=73|issue=4|pages=889–910|doi=10.1016/j.gca.2008.10.036|bibcode=2009GeCoA..73..889B|s2cid=59065579 }}</ref> It was discovered at [[Birness]], [[Aberdeenshire]], [[Scotland]].

Its precipitation from the oxidation of [[Manganese|Mn(II)]] in oxygenated aqueous solutions is kinetically hindered and slow on mineral surfaces. Biological [[Manganese|Mn(II)]] oxidation is generally fast relative to abiotic [[Manganese|Mn(II)]] oxidation processes, and for this reason the majority of natural birnessites is believed to be produced by [[microorganism]]s, especially [[bacteria]], but also [[Fungus|fungi]].<ref name="Tebo_2004">{{Cite journal|last1=Tebo|first1=B. M.|display-authors=1|last2=Bargar|first2=J.R.|last3=Clement|first3=Brian G.|last4=Dick|first4=Gregory J.|last5=Murray|first5=Karen J.|last6=Parker|first6=Dorothy|last7=Verity|first7=Rebecca|last8=Webb|first8=Samuel M.|date=2004-05-19|title=Biogenic manganese oxides: Properties and mechanisms of formation|url=http://www.annualreviews.org/doi/10.1146/annurev.earth.32.101802.120213|journal=Annual Review of Earth and Planetary Sciences|language=en|volume=32|pages=287–328|doi=10.1146/annurev.earth.32.101802.120213|bibcode=2004AREPS..32..287T}}</ref>

Birnessite is a [[non-stoichiometric compound]], in which variable amounts of [[Manganese|Mn⁴⁺]] ions in the nominal MnO₂·''n''H₂O formula either are missing, or are replaced primarily by [[Manganese|Mn³⁺]] ions and secondarily by [[Manganese|Mn²⁺]] ions. Because a solid is overall electrically neutral, birnessite contains foreign cations to balance the net negative charge created by [[Manganese|Mn⁴⁺]] vacancies and heterovalent Mn substitutions.

Two [[Crystallography|crystallographic]] structures are known, [[Triclinic crystal system|triclinic]] birnessite (TcBi)<ref name=":2">{{Cite journal|last1=Lanson|first1=B|display-authors=1|last2=Drits|first2=V. A.|last3=Feng|first3=Qi|last4=[[Alain Manceau|Manceau]]|first4=A|date=2002|title=Structure of synthetic Na-birnessite: Evidence for a triclinic one-layer unit cell|url=http://dx.doi.org/10.2138/am-2002-11-1215|journal=American Mineralogist|volume=87|issue=11–12|pages=1662–1671|doi=10.2138/am-2002-11-1215|bibcode=2002AmMin..87.1662L|s2cid=53443294}}</ref> and [[Hexagonal crystal family|hexagonal]] birnessite (HBi).<ref name=":3">{{Cite journal|last1=Drits|first1=V. A.|display-authors=1|last2=Silvester|first2=E.|last3=Gorshkov|first3=Anatoli I.|last4=[[Alain Manceau|Manceau]]|first4=A|date=1997|title=Structure of synthetic monoclinic Na-rich birnessite and hexagonal birnessite; I, Results from X-ray diffraction and selected-area electron diffraction|url=http://dx.doi.org/10.2138/am-1997-9-1012|journal=American Mineralogist|volume=82|issue=9–10|pages=946–961|doi=10.2138/am-1997-9-1012|bibcode=1997AmMin..82..946D|s2cid=56030552}}</ref><ref name=":4">{{Cite journal|last1=Silvester|first1=E.|display-authors=1|last2=[[Alain Manceau|Manceau]]|first2=A|last3=Drits|first3=V. A.|date=1997|title=Structure of synthetic monoclinic Na-rich birnessite and hexagonal birnessite; II, Results from chemical studies and EXAFS spectroscopy|url=http://dx.doi.org/10.2138/am-1997-9-1013|journal=American Mineralogist|volume=82|issue=9–10|pages=962–978|doi=10.2138/am-1997-9-1013|bibcode=1997AmMin..82..962S|s2cid=55969753}}</ref><ref name=":5">{{Cite journal|last1=Lanson|first1=B|display-authors=1|last2=Drits|first2=V. A.|last3=Silvester|first3=E.|last4=[[Alain Manceau|Manceau]]|first4=A|date=2000|title=Structure of H-exchanged hexagonal birnessite and its mechanism of formation from Na-rich monoclinic buserite at low pH|url=http://dx.doi.org/10.2138/am-2000-5-625|journal=American Mineralogist|volume=85|issue=5–6|pages=826–838|doi=10.2138/am-2000-5-625|bibcode=2000AmMin..85..826L|s2cid=55586944}}</ref> The two of them consist of layers of edge-sharing MnO₆ octahedra separated by one or two layers of [[water]] molecules. The one-[[water]] layer compounds have a characteristic ~7 [[Angstrom|Å]] repeat in the layer stacking direction, and addition of a second [[water]] layer expands the layer spacing to ~10 [[Angstrom|Å]]. The 10 [[Angstrom|Å]] form is named [[buserite]].

The layer composition of TcBi is typically Mn⁴⁺_0.69Mn³⁺_0.31. The Mn³⁺O₆ and Mn⁴⁺O₆ octahedra are fully ordered in raws in the MnO₂ layers, such that every [[Manganese|Mn³⁺]]-rich row alternates with two [[Manganese|Mn⁴⁺]]-rich rows.^10,11 The layer charge is offset by alkaline and alkali-earth cations (e.g., Na, K, Ca, Ba) into the interlayer region along with [[water]] molecules, and therefore TcBi has a [[cation-exchange capacity]]. A typical chemical formula of [[Sodium|Na]]-exchanged TcBi is Na_0.31(Mn⁴⁺_0.69 Mn³⁺_0.31)O₂·0.4H₂O.<ref name=":2" />

The layer structure of HBi differs from that of TcBi by the presence of octahedral [[Manganese|Mn⁴⁺]] vacancies (Vac). The chemical formula of synthetic HBi depends on [[pH]]. The generic formula is H⁺''_x'' Mn³⁺''_y'' Mn²⁺''_z'' (Mn⁴⁺''_u'' Mn³⁺''_v''Vac''_w'')O₂, with ''x'' + 3''y'' + 2''z'' = ''v'' + 4''w'' for neutrality.<ref name=":3" /><ref name=":4" /><ref name=":5" />

The MnO₂ layers are stacked periodically in synthetic [[Triclinic crystal system|triclinic]] and [[Hexagonal crystal family|hexagonal]] birnessite [[crystal]]s. It is, however, rarely the case in natural materials. In addition to being chemically complex, natural birnessite [[crystal]]scrystals are structurally disordered with respect to the layer stacking and the flatness of the layers.<ref>{{Cite journal|last1=[[Alain Manceau|Manceau]]|first1=A|display-authors=1|last2=Marcus|first2=Matthew A.|last3=Grangeon|first3=S.|last4=Lanson|first4=M.|last5=Lanson|first5=B.|last6=Gaillot|first6=A.-C.|last7=Skanthakumar|first7=S.|last8=Soderholm|first8=L.|date=2013-02-01|title=Short-range and long-range order of phyllomanganate nanoparticles determined using high-energy X-ray scattering|url=http://scripts.iucr.org/cgi-bin/paper?S0021889812047917|journal=Journal of Applied Crystallography|volume=46|issue=|pages=193–209|doi=10.1107/S0021889812047917|s2cid=56356250|issn=}}</ref> A natural birnessite crystal may contain only a few layers, and they are often bent and always imperfectly stacked with orientational and translational loss of registry. The stacking disorder is referred to as “turbostratic”"turbostratic" when the layers are oriented completely at random. Natural birnessite with turbostratically stacked layers is named vernadite,<ref>{{Cite journal|last=Giovanoli|first=R.|date=1980|title=Vernadite is random-stacked birnessite|url=http://dx.doi.org/10.1007/bf00206520|journal=Mineralium Deposita|volume=15|issue=2|pages=251–253|doi=10.1007/bf00206520|bibcode=1980MinDe..15..251G|s2cid=104363781}}</ref><ref>{{Cite journal|last1=[[Alain Manceau|Manceau]]|first1=A.|display-authors=1|last2=Combes|first2=J. M.|date=1988|title=Structure of Mn and Fe oxides and oxyhydroxides: A topological approach by EXAFS|url=http://dx.doi.org/10.1007/bf00307518|journal=Physics and Chemistry of Minerals|volume=15|issue=3|pages=283–295|doi=10.1007/bf00307518|bibcode=1988PCM....15..283M|s2cid=97465847}}</ref><ref>{{Cite journal|last=Hochella|first=M. F.|date=2005|title=Environmentally important, poorly crystalline Fe/Mn hydrous oxides: Ferrihydrite and a possibly new vernadite-like mineral from the Clark Fork River Superfund Complex|url=http://dx.doi.org/10.2138/am.2005.1591|journal=American Mineralogist|volume=90|issue=4|pages=718–724|doi=10.2138/am.2005.1591|bibcode=2005AmMin..90..718H|s2cid=54664549}}</ref> and the synthetic analog is named δ-MnO₂. The layer spacing of vernadite can be also ~7 [[Angstrom|Å]] or ~10 [[Angstrom|Å]], and interstratification of the two types of layers has been observed on quartz coatings<ref name=":1" /> and in ferromanganese crusts.<ref>{{Cite journal|last1=Lee|first1=S|display-authors=1|last2=Xu|first2=Hfang|last3=Xu|first3=Wenqian|last4=Sun|first4=Xiaoming|date=2019|title=The structure and crystal chemistry of vernadite in ferromanganese crusts|url=https://scripts.iucr.org/cgi-bin/paper?S2052520619006528|journal=Acta Crystallographica Section B|volume=75|issue=4|pages=591–598|doi=10.1107/S2052520619006528|pmid=32830716|osti=1559941|s2cid=202084338}}</ref>

The +4 charge deficit of a vacancy can be balanced by a large variety of interlayer cations forming [[Inner sphere complex|inner-sphere complexes]] above and below the vacancies (e.g., [[Calcium|Ca]], [[Copper|Cu]], [[Zinc|Zn]], [[Lead|Pb]], [[Cadmium|Cd]], [[Thallium|Tl]]).<ref name=":0" /><ref>{{Cite journal|last1=Lanson|first1=B|display-authors=1|last2=Drits|first2=V. A.|last3=Gaillot|first3=Anne-Claire|last4=Silvester|first4=E.|last5=Plançon|first5=A|last6=[[Alain Manceau|Manceau]]|first6=A|date=2002|title=Structure of heavy-metal sorbed birnessite: Part 1. Results from X-ray diffraction|url=http://dx.doi.org/10.2138/am-2002-11-1213|journal=American Mineralogist|volume=87|issue=11–12|pages=1631–1645|doi=10.2138/am-2002-11-1213|bibcode=2002AmMin..87.1631L|s2cid=52255943}}</ref><ref>{{Cite journal|last1=Drits|first1=V. 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W.|date=1975|title=The interaction of metal ions at the manganese dioxide-solution interface|url=https://linkinghub.elsevier.com/retrieve/pii/0016703775901039|journal=Geochimica et Cosmochimica Acta|language=en|volume=39|issue=4|pages=505–519|doi=10.1016/0016-7037(75)90103-9|bibcode=1975GeCoA..39..505M}}</ref> and theoretically by surface complexation modeling<ref name="Appelo_Postma_1999">{{Cite journal|last1=Appelo|first1=C.A.J.|display-authors=1|last2=Postma|first2=D.|date=1999|title=A consistent model for surface complexation on birnessite (δ-MnO₂) and its application to a column experiment|url=http://dx.doi.org/10.1016/s0016-7037(99)00231-8|journal=Geochimica et Cosmochimica Acta|volume=63|issue=19–20|pages=3039–3048|doi=10.1016/s0016-7037(99)00231-8|bibcode=1999GeCoA..63.3039A}}</ref> and computational chemistry.<ref>{{Cite journal|last1=Kwon|first1=K. D.|display-authors=1|last2=Refson|first2=Keith|last3=Sposito|first3=Garrison|date=2013|title=Understanding the trends in transition metal sorption by vacancy sites in birnessite|url=http://dx.doi.org/10.1016/j.gca.2012.08.038|journal=Geochimica et Cosmochimica Acta|volume=101|pages=222–232|doi=10.1016/j.gca.2012.08.038|bibcode=2013GeCoA.101..222K}}</ref><ref>{{Cite journal|last1=[[Alain Manceau|Manceau]]|first1=A|display-authors=1|last2=Steinmann|first2=Stephan N.|date=2021|title=Nature of High- and Low-Affinity Metal Surface Sites on Birnessite Nanosheets|url=https://pubs.acs.org/doi/10.1021/acsearthspacechem.0c00278|journal=ACS Earth and Space Chemistry|language=en|volume=5|issue=1|pages=66–76|doi=10.1021/acsearthspacechem.0c00278|bibcode=2021ESC.....5...66M|s2cid=234304816}}</ref> [[Lead|Pb²⁺]] has the highest stability at the HBi surface, and the high geochemical affinity of [[Lead|Pb²⁺]] for birnessite probably explains its billion-fold enrichment in marine ferromanganese deposits compared to [[seawater]], which surpasses those of all other elements.<ref name=":6">{{Citation|last1=Hein|first1=J.R.|title=Deep-Ocean Ferromanganese Crusts and Nodules|date=2014|url=http://dx.doi.org/10.1016/b978-0-08-095975-7.01111-6|work=Treatise on Geochemistry|pages=273–291|publisher=Elsevier|access-date=2021-09-26|display-authors=1|last2=Koschinsky|first2=A.|doi=10.1016/b978-0-08-095975-7.01111-6|isbn=9780080983004}}</ref>

[[Transition metal]] cations sorbed on vacancies were also observed to enter the underlying vacancies and become incorporated into the MnO₂ layer, when their effective ionic radius<ref>{{Cite journal|last=Shannon|first=R. D.|date=1976|title=Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides|url=http://dx.doi.org/10.1107/s0567739476001551|journal=Acta Crystallographica Section A|volume=32|issue=5|pages=751–767|doi=10.1107/s0567739476001551|bibcode=1976AcCrA..32..751S}}</ref> is close to that of [[Manganese|Mn⁴⁺]] (r = 0.53 [[Angstrom|Å]]). For example, [[Zinc|Zn²⁺]] (r = 0.74 [[Angstrom|Å]]) was never observed to enter a vacancy site, while [[Nickel|Ni²⁺]] (r = 0.69 [[Angstrom|Å]]) partly enters, and [[Cobalt|Co³⁺]] (r = 0.54 [[Angstrom|Å]]) always does.<ref name=":1" /><ref name="Manceau_1997">{{Cite journal|last1=[[Alain Manceau|Manceau]]|first1=A|display-authors=1|last2=Drits|first2=V. A.|last3=Silvester|first3=E.|last4=Bartoli|first4=Celine|last5=Lanson|first5=B|date=1997|title=Structural mechanism of Co²⁺ oxidation by the phyllomanganate buserite|url=http://dx.doi.org/10.2138/am-1997-11-1213|journal=American Mineralogist|volume=82|issue=11–12|pages=1150–1175|doi=10.2138/am-1997-11-1213|bibcode=1997AmMin..82.1150M|s2cid=54923713}}</ref><ref>{{Cite journal|last1=Peacock|first1=C. L.|display-authors=1|last2=Sherman|first2=D. M.|date=2007|title=Crystal-chemistry of Ni in marine ferromanganese crusts and nodules|url=http://dx.doi.org/10.2138/am.2007.2378|journal=American Mineralogist|volume=92|issue=7|pages=1087–1092|doi=10.2138/am.2007.2378|bibcode=2007AmMin..92.1087P|s2cid=98074547}}</ref> Octahedral high-spin [[Cobalt|Co²⁺]] (r = 0.74 [[Angstrom|Å]]) sorbed on a vacancy is transformed into a smaller tetrahedral complex (r = 0.58 [[Angstrom|Å]]) to penetrate into the octahedral Mn vacancy, and is subsequently converted to the low-spin state before being oxidized to [[Cobalt|Co³⁺]] by Mn⁴⁺, which is reduced to Mn³⁺.<ref>{{Cite journal|last1=[[Alain Manceau|Manceau]]|first1=A.|last2=Steinmann|first2=S.|date=2022|title=Density Functional Theory Modeling of the Oxidation Mechanism of Co(II) by Birnessite|url=https://doi.org/10.1021/acsearthspacechem.2c00122|journal=ACS Earth and Space Chemistry|volume=6|issue=8 |pages=2063–2075|doi=10.1021/acsearthspacechem.2c00122|bibcode=2022ESC.....6.2063M |s2cid=251086409 }}</ref> The surface-catalyzed, redox-driven uptake of [[Cobalt|Co]] leads also to a billion-fold enrichment in marine ferromanganese deposits compared to [[seawater]]. The geochemical partitioning of [[Cobalt|Co]] between ferromanganese deposits and [[seawater]] is the second-highest of all elements after [[Lead|Pb²⁺]].<ref name=":6" />

In nature, photosynthetic organisms use the high oxidative ability of birnessite-type Mn₄CaO₅ clusters to oxidize [[water]] into molecular oxygen through the [[photosystem II]] membrane protein complex.<ref>{{Cite journal|last1=Chernev|first1=P.|display-authors=1|last2=Fischer|first2=Sophie|last3=Hoffmann|first3=Jutta|last4=Oliver|first4=Nicholas|last5=Assunção|first5=Ricardo|last6=Yu|first6=Boram|last7=Burnap|first7=Robert L.|last8=Zaharieva|first8=Ivelina|last9=Nürnberg|first9=Dennis J.|last10=Haumann|first10=Michael|last11=Dau|first11=Holger|date=2021|title=Publisher Correction: Light-driven formation of manganese oxide by today's photosystem II supports evolutionarily ancient manganese-oxidizing photosynthesis|url=http://dx.doi.org/10.1038/s41467-020-20868-9|journal=Nature Communications|volume=12|issue=1|page=419|doi=10.1038/s41467-020-20868-9|pmid=33436628|pmc=7804171}}</ref>

Because of their [[Semiconductor|semiconducting]] properties, birnessite-type materials are used in a variety of areas, including [[catalysis]] and [[Electrochemistry|electrochemical]] energy storage ([[Electric battery|batteries]] and [[pseudocapacitor]]s). The ordering of the [[Manganese|Mn³⁺]] cations in [[Triclinic crystal system|triclinic]] birnessite, and the [[Manganese|Mn⁴⁺]] vacancies in [[Hexagonal crystal family|hexagonal]] birnessite, both reduce the [[band gap]],<ref>{{Cite journal|last1=Lucht|first1=K. P.|display-authors=1|last2=Mendoza-Cortes|first2=Jose L.|date=2015|title=Birnessite: A Layered Manganese Oxide To Capture Sunlight for Water-Splitting Catalysis|url=http://dx.doi.org/10.1021/acs.jpcc.5b07860|journal=The Journal of Physical Chemistry C|volume=119|issue=40|pages=22838–22846|doi=10.1021/acs.jpcc.5b07860}}</ref><ref>{{Cite journal|last1=Kwon|first1=K. D.|display-authors=1|last2=Refson|first2=Keith|last3=Sposito|first3=Garrison|date=2008|title=Defect-Induced Photoconductivity in Layered Manganese Oxides: A Density Functional Theory Study|url=http://dx.doi.org/10.1103/physrevlett.100.146601|journal=Physical Review Letters|volume=100|issue=14|page=146601|doi=10.1103/physrevlett.100.146601|pmid=18518059|bibcode=2008PhRvL.100n6601K|s2cid=2146794 }}</ref><ref>{{Cite journal|last1=Gao|first1=P.|display-authors=1|last2=Chen|first2=Zhen|last3=Gong|first3=Yuxuan|last4=Zhang|first4=Rui|last5=Liu|first5=H|last6=Tang|first6=Pei|last7=Chen|first7=Xiaohua|last8=Passerini|first8=Stefano|last9=Liu|first9=Jilei|date=2020|title=The Role of Cation Vacancies in Electrode Materials for Enhanced Electrochemical Energy Storage: Synthesis, Advanced Characterization, and Fundamentals|url=http://dx.doi.org/10.1002/aenm.201903780|journal=Advanced Energy Materials|volume=10|issue=14|pages=1903780|doi=10.1002/aenm.201903780|s2cid=214006754}}</ref> and therefore enhance [[Electrical resistivity and conductivity|electrical conductivity]]. Half-[[Metallic bonding|metallic]] behavior was observed for MnO₂ nanosheets with [[Manganese|Mn]] vacancies, rendering them promising candidates for applications in [[spintronics]].<ref>{{Cite journal|last1=Wang|first1=H|display-authors=1|last2=Zhang|first2=Jiajia|last3=Hang|first3=Xudong|last4=Zhang|first4=Xiaodong|last5=Xie|first5=Junfeng|last6=Pan|first6=Bicai|last7=Xie|first7=Yi|date=2014|title=Half-Metallicity in Single-Layered Manganese Dioxide Nanosheets by Defect Engineering|url=http://dx.doi.org/10.1002/ange.201410031|journal=Angewandte Chemie|volume=127|issue=4|pages=1211–1215|doi=10.1002/ange.201410031}}</ref>

File:Baltic nodule.jpg|[[X-ray fluorescence]] tricolor map of a [[ferromanganese nodules|ferromanganese nodule]] from the [[Baltic seaSea]].

* [[TodorokitePyrolusite]]