{{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 | 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 | class = Ditetragonal dipyramidal (4/mmm) <br/>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 fluoride mineral with the formula MgF<sub>2</sub>. It crystallizes in the tetragonal crystal system, typically as clear to white vitreous prisms. It may be fibrous and occur as radiating aggregates. It has a Mohs hardness of 5 to 6 and a specific gravity of 2.97 to 3.15. 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 (1827–1884). Its type locality is the {{interlanguage link|glacier de Gébroulaz|fr}} in France, where it occurred inside bitumen-bearing dolomite-anhydrite clasts within a moraine deposit. It has been reported in an evaporite deposit at Bleicherode; within volcanic ejecta and fumaroles at Vesuvius; in a metamorphic magnesite deposit at {{interlanguage link|Serra das Éguas|pt}}; and in sodic alkali 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

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