| Combeite | |
| Category: | Silicate mineral |
| Formula: | Na2Ca2Si3O9 |
| Imasymbol: | Cbe[1] |
| Strunz: | 9.CJ.15a |
| System: | Trigonal |
| Class: | Trapezohedral (32) (same H-M symbol) |
| Symmetry: | P3121 |
| Unit Cell: | a = 10.42 Å, c = 13.14 Å; Z = 6 |
| Color: | Colorless |
| Habit: | Stout prisms |
| Streak: | White |
| Diaphaneity: | Transparent |
| Gravity: | 2.844 |
| Opticalprop: | Uniaxial (+) |
| Refractive: | nω = 1.598 nε = 1.598 |
| Birefringence: | δ = 0.000 |
| References: | [2] |
Combeite is a rare silicate mineral with the formula Na2Ca2Si3O9. It has a trigonal crystal system.
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]