# Sellaite

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> Markdown URL: https://mediated.wiki/source/Sellaite.md
> Source: https://en.wikipedia.org/wiki/Sellaite
> Source revision: 1338129068
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{{Short description|Halide mineral}}
{{infobox mineral
| name        = Sellaite
| boxwidth    = 
| boxbgcolor  = 
| image       = Sellaite-39033.jpg
| imagesize   = 150px
| alt         = 
| caption     = Sellaite crystal from Serra das Éguas, Brazil (size: 4.2 × 2.4 × 2 cm)
| category    = [Halide mineral](/source/Halide_mineral)
| formula     = MgF<sub>2</sub>
| IMAsymbol   = Sel<ref>{{Cite journal |last=Warr |first=L. N. |date=2021 |title=IMA–CNMNC approved mineral symbols |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}}</ref>
| molweight   = 
| strunz      = 3.AB.15
| dana        = 
| system      = [Tetragonal](/source/Tetragonal)
| class       = Ditetragonal dipyramidal (4/mmm) <br/>[H-M symbol](/source/H-M_symbol): (4/m 2/m 2/m)
| symmetry    = ''P''4<sub>2</sub>/mnm
| unit cell   = ''a'' = 4.6213(2)&nbsp;Å<br/> ''c'' = 3.0519(1)&nbsp;Å<br/> ''Z''&nbsp;=&nbsp;2
| color       = Colorless to white
| colour      = 
| habit       = Prismatic crystals; fibrous, radial, spherulitic 
| twinning    = On {011}
| cleavage    = Perfect on {010} and {110}
| fracture    = Conchoidal
| tenacity    = Brittle
| mohs        = 5–5.5
| luster      = Vitreous
| streak      = 
| diaphaneity = Transparent
| gravity     = 3.15
| density     = 
| polish      = 
| opticalprop = Uniaxial (+)
| refractive  = ''n<sub>ω</sub>'' = 1.378<br/>''n<sub>ε</sub>'' = 1.390
| birefringence = δ = 0.012
| pleochroism = 
| 2V          = 
| dispersion  = 
| extinction  = 
| length fast/slow =
| fluorescence = 
| absorption  = 
| melt        = 
| fusibility  = 
| diagnostic  = 
| solubility  = 
| impurities  = 
| alteration  = 
| references  = <ref name=HBM>[http://rruff.geo.arizona.edu/doclib/hom/sellaite.pdf Mineral Data Publishing: Handbook of Mineralogy]</ref><ref name=Mindat>[http://www.mindat.org/min-3614.html Mindat with location data].</ref><ref name=Webmin>[http://webmineral.com/data/Sellaite.shtml Webmineral data].</ref>
}}
'''Sellaite''' is a [magnesium](/source/magnesium) [fluoride](/source/fluoride) mineral with the formula MgF<sub>2</sub>. It crystallizes in the [tetragonal](/source/tetragonal) [crystal system](/source/crystal_system), typically as clear to white [vitreous](/source/vitrification) prisms. It may be fibrous and occur as radiating [aggregate](/source/Aggregate_(geology))s. It has a [Mohs hardness](/source/Mohs_hardness) of 5 to 6 and a [specific gravity](/source/specific_gravity) of 2.97 to 3.15. [Refractive index](/source/Refractive_index) values are ''n<sub>ω</sub>'' = 1.378 and ''n<sub>ε</sub>'' = 1.390.

==Discovery and occurrence==
Sellaite was first described in 1868 and named for Italian mining engineer and mineralogist [Quintino Sella](/source/Quintino_Sella) (1827–1884). Its [type locality](/source/Type_locality_(geology)) is the {{interlanguage link|glacier de Gébroulaz|fr}} in France, where it occurred inside [bitumen](/source/bitumen)-bearing [dolomite](/source/Dolomite_(rock))-[anhydrite](/source/anhydrite) [clast](/source/clast)s within a [moraine](/source/moraine) deposit. It has been reported in an [evaporite](/source/evaporite) deposit at [Bleicherode](/source/Bleicherode); within [volcanic](/source/volcanic) [ejecta](/source/ejecta) and [fumarole](/source/fumarole)s at [Vesuvius](/source/Vesuvius); in a [metamorphic](/source/metamorphism) [magnesite](/source/magnesite) deposit at {{interlanguage link|Serra das Éguas|pt}}; and in [sodic alkali](/source/alkali_soil) [granite](/source/granite) near {{interlanguage link|Gjerdingen|no}}.<ref name=HBM/><ref name=Mindat/>

==References==
{{Reflist}}
* Palache, C., H. Berman, and C. Frondel (1951) ''Dana’s system of mineralogy,'' (7th edition), v. II, pp. 37–39

Category:Magnesium minerals
Category:Fluorine minerals
Category:Tetragonal minerals
Category:Minerals in space group 136

{{Halide-mineral-stub}}

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Adapted from the Wikipedia article [Sellaite](https://en.wikipedia.org/wiki/Sellaite) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Sellaite?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.