{{Short description|Silicate mineral}} {{infobox mineral | name = Combeite | image = Combeite.jpg | alt = | caption = Pale pink crystal aggregates of the very rare silicate mineral combeite from one of the only 4 localities known worldwide: Mount Oldoinyo Lengai, Arusha Region, Tanzania. | category = Silicate mineral | formula = Na<sub>2</sub>Ca<sub>2</sub>Si<sub>3</sub>O<sub>9</sub> | IMAsymbol=Cbe<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> | strunz = 9.CJ.15a | dana = | system = Trigonal | class = Trapezohedral (32) <br><small>(same H-M symbol)</small> | symmetry = ''P3''<sub>1</sub>21 | unit cell = a = 10.42&nbsp;Å, c = 13.14&nbsp;Å; Z&nbsp;=&nbsp;6 | color = Colorless | habit = Stout prisms | twinning = | cleavage = | fracture = | tenacity = | mohs = | luster = | streak = White | diaphaneity = Transparent | gravity = 2.844 | density = | polish = | opticalprop = Uniaxial (+) | refractive = n<sub>ω</sub> = 1.598 n<sub>ε</sub> = 1.598 | birefringence = δ = 0.000 | pleochroism = | 2V = | dispersion = | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | fusibility = | diagnostic = | solubility = | impurities = | alteration = | other = | prop1 = | prop1text = | references = <ref>[https://www.mineralienatlas.de/lexikon/index.php/MineralData?mineral=Combeite Mineralienatlas]</ref><ref name=Mindat/><ref name=Webmin/> }} '''Combeite''' is a rare silicate mineral with the formula Na<sub>2</sub>Ca<sub>2</sub>Si<sub>3</sub>O<sub>9</sub>. It has a trigonal crystal system.

==Discovery and occurrence== It was first described in 1957 for an occurrence in nephelinite lavas and tephra on Mount Nyiragongo, Goma, Kivu, Democratic Republic of Congo (then Zaïre).<ref name=Mindat>[http://www.mindat.org/min-1115.html Combeite on Mindat.org]</ref> It has also been reported from the Bellerberg volcano in Ettringen, Germany and the Oldoinyo Lengai volcano, Tanzania.<ref name=Mindat/> It was named for Arthur Delmar Combe of the Geological Survey of Uganda.<ref name=Webmin>[http://www.webmineral.com/data/Combeite.shtml Combeite data from Webmineral]</ref><ref name=HBM>[http://rruff.geo.arizona.edu/doclib/hom/combeite.pdf Handbook of Mineralogy]</ref>

It is associated with götzenite at Mount Shaheru, Congo; and with wollastonite, clinopyroxene, nepheline, melilite, titanian garnet and titanian magnetite at Oldoinyo Lengai.<ref name=HBM/>

== References == {{Reflist}}

Category:Sodium minerals Category:Calcium minerals Category:Cyclosilicates Category:Trigonal minerals Category:Minerals in space group 152 or 154

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