Combeite
Appearance
Combeite | |
---|---|
![]() 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. | |
General | |
Category | Silicate mineral |
Formula (repeating unit) | Na2Ca2Si3O9 |
IMA symbol | Cbe[1] |
Strunz classification | 9.CJ.15a |
Crystal system | Trigonal |
Crystal class | Trapezohedral (32) (same H-M symbol) |
Space group | P3121 |
Unit cell | a = 10.42 Å, c = 13.14 Å; Z = 6 |
Identification | |
Color | Colorless |
Crystal habit | Stout prisms |
Streak | White |
Diaphaneity | Transparent |
Specific gravity | 2.844 |
Optical properties | Uniaxial (+) |
Refractive index | nω = 1.598 nε = 1.598 |
Birefringence | δ = 0.000 |
References | [2][3][4] |
Combeite is a rare silicate mineral with the formula Na2Ca2Si3O9. It has a trigonal crystal system.
Discovery and occurrence
[edit]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
[edit]- ^ 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.
- ^ Mineralienatlas
- ^ a b c Combeite on Mindat.org
- ^ a b Combeite data from Webmineral
- ^ a b Handbook of Mineralogy