View source for Boehmite

{{Short description|Mineral}}
{{Infobox mineral
| name        = Boehmite
| category    = [[Oxide mineral]]
| image       = Böhmite-89904.jpg
| imagesize   = 260px
| alt         = 
| caption     = Böhmite and [[Natrolite]] from Sagåsen (Strandåsen), Mørje, Porsgrunn, Telemark, Norway (Field of view 10 mm)
| formula     = γ-AlO(OH)
| IMAsymbol=Bhm<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|url=https://www.cambridge.org/core/journals/mineralogical-magazine/article/imacnmnc-approved-mineral-symbols/62311F45ED37831D78603C6E6B25EE0A|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free|url-access=subscription}}</ref>
| molweight   = 
| strunz      = 4.FE.15
| dana        = 6.1.2.1
| system      = [[Orthorhombic]]
| class       = Dipyramidal (mmm) <br/>[[H-M symbol]]: (2/m 2/m 2/m)
| symmetry    = ''Amam''
| unit cell   = a = 3.693&nbsp;[[Ångstrom|Å]], <br/>b = 12.221&nbsp;Å, <br/>c = 2.865&nbsp;Å; Z&nbsp;=&nbsp;4
| color       = White, pale greyish brown; yellowish or reddish when impure; colorless in thin section
| colour      = 
| habit       = Tabular crystal rare, fine grained in pisolitic aggregates or disseminated
| twinning    = 
| cleavage    = Very good on {010}, good on {100}, and poor on {001}
| fracture    = Uneven
| tenacity    = Brittle 
| mohs        = 3.5
| luster      = Vitreous, pearly on {010}
| streak      = White
| diaphaneity = Translucent
| gravity     = 3.02–3.05
| density     =  
| polish      = 
| opticalprop = Biaxial (+)
| refractive  = n<sub>α</sub> = 1.644 – 1.648 n<sub>β</sub> = 1.654 – 1.657 n<sub>γ</sub> = 1.661 – 1.668
| birefringence = δ = 0.017 – 0.020
| pleochroism = 
| 2V          = Measured: 74° to 88°, Calculated: 80° 
| dispersion  = weak
| extinction  = 
| length fast/slow =
| fluorescence= 
| absorption  =
| melt        = 
| fusibility  = 
| diagnostic  = 
| solubility  = 
| other       = 
| alteration  = 
| references  = <ref name=Webmin>{{cite web|url=http://webmineral.com/data/Boehmite.shtml|title=Boehmite|publisher=Webmineral data|accessdate=2010-07-10}}</ref><ref name=Mindat>{{cite web|url=http://www.mindat.org/min-707.html|title=Boehmite|publisher=Mindat with location data|accessdate=2010-07-10}}</ref><ref name=Handbook>[http://rruff.geo.arizona.edu/doclib/hom/bohmite.pdf Mineral Data Pub. Handbook of Mineralogy]</ref><ref>{{cite web|url=http://www.minerals.net/mineral/boehmite.aspx|title=The Mineral Boehmite|publisher=minerals.net|accessdate=June 10, 2014}}</ref>}}

'''Boehmite''' or '''böhmite''' is an [[aluminium oxide hydroxide]] (γ-AlO(OH)) mineral, a component of the [[aluminium]] ore [[bauxite]]. It is [[Dimorphism (crystallography)|dimorphous]] with [[diaspore]]. It crystallizes in the [[orthorhombic]] dipyramidal system and is typically massive in habit. It is white with tints of yellow, green, brown or red due to impurities. It has a vitreous to pearly luster, a [[Mohs hardness]] of 3 to 3.5 and a [[specific gravity]] of 3.00 to 3.07. It is colorless in thin section, optically biaxial positive with [[Refractive index|refractive indices]] of nα = 1.644 – 1.648, nβ = 1.654 – 1.657 and nγ = 1.661 – 1.668.

Boehmite occurs in tropical [[laterite]]s and bauxites developed on [[Aluminosilicate|alumino-silicate]] bedrock. It also occurs as a [[hydrothermal alteration]] product of [[corundum]] and [[nepheline]]. It occurs with [[kaolinite]], [[gibbsite]] and diaspore in bauxite deposits; and with nepheline, gibbsite, diaspore, [[natrolite]] and [[analcime]] in nepheline [[pegmatite]]s.<ref name=Handbook/> Industrially, it is used as an inexpensive [[flame retardant]] additive for [[fire-safe polymers]].

It was first described by J. de Lapparent in 1927 for an occurrence in the bauxites of Mas Rouge, [[Les Baux-de-Provence]], [[France]], and named<ref>{{cite journal |title=Natural boehmite single crystals from Ceylon|journal=Contributions to Mineralogy and Petrology|volume=39|issue=2|pages=171|date=1973|bibcode=1973CoMP...39..171S|last1=Sahama|first1=Th. G.|last2=Lehtinen|first2=Martti|last3=Rehtijärvi|first3=Pentti|doi=10.1007/BF00375738|s2cid=129237343}}</ref> for the Bohemian-German chemist [[Johann Böhm (chemist)|Johann Böhm]]  (1895–1952) who carried out X-ray studies of aluminium oxide hydroxides in 1925<ref>{{cite journal |doi=10.1002/zaac.19251490114|title=Über Aluminium- und Eisenhydroxyde. I|journal=Zeitschrift für anorganische und allgemeine Chemie|volume=149|pages=203–216|year=1925|last1=Böhm|first1=J.}}</ref> (and not for the German geologist [[Johannes Böhm (geologist)|Johannes Böhm]] (1857–1938) as often stated).<ref name=Webmin/><ref name=Mindat/>

==See also==
*[[List of minerals]]
*[[List of minerals named after people]]
*[[Pseudoboehmite]]

==References==
{{Reflist}}

*[https://web.archive.org/web/20070210012812/http://www.uwgb.edu/dutchs/PETROLGY/LepidocrStruc.HTM Steven Dutch, 2002, Lepidocrocite and Boehmite Structure, University of Wisconsin – Green Bay]

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[[Category:Hydroxide minerals]]
[[Category:Aluminium minerals]]
[[Category:Orthorhombic minerals]]
[[Category:Minerals in space group 63]]