Combeite

Silicate mineral
(repeating unit)Na2Ca2Si3O9IMA symbolCbe[1]Strunz classification9.CJ.15aCrystal systemTrigonalCrystal classTrapezohedral (32)
(same H-M symbol)Space groupP3121Unit cella = 10.42 Å, c = 13.14 Å; Z = 6IdentificationColorColorlessCrystal habitStout prismsStreakWhiteDiaphaneityTransparentSpecific gravity2.844Optical propertiesUniaxial (+)Refractive indexnω = 1.598 nε = 1.598Birefringenceδ = 0.000References[2][3][4]

Combeite is a rare silicate mineral with the formula Na2Ca2Si3O9. 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).[3] It has also been reported from the Bellerberg volcano in Ettringen, Germany and the Oldoinyo Lengai volcano, Tanzania.[3] It was named for Arthur Delmar Combe of the Geological Survey of Uganda.[4][5]

It is associated with götzenite at Mount Shaheru, Congo; and with wollastonite, clinopyroxene, nepheline, melilite, titanian garnet and titanian magnetite at Oldoinyo Lengai.[5]

References

  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ Mineralienatlas
  3. ^ a b c Combeite on Mindat.org
  4. ^ a b Combeite data from Webmineral
  5. ^ a b Handbook of Mineralogy


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