Alluaivite
| Alluaivite | |
|---|---|
| General | |
| Category | Silicate mineral, Cyclosilicate |
| Formula | Na19(Ca,Mn)6(Ti,Nb)3Si26O74Cl·2H2O |
| IMA symbol | Aav |
| Strunz classification | 9.CO.10 (10 ed) 8/E.25-40 (8 ed) |
| Dana classification | 64.1b.1.1 |
| Crystal system | Trigonal |
| Crystal class | Hexagonal scalenohedral (3m) H-M symbol: (3 2/m) |
| Space group | R3m |
| Unit cell | a = 14.04, c = 60.6 [Å]; Z = 6 |
| Identification | |
| Color | Colorless to weak brownish pink |
| Crystal habit | irregular accumulations |
| Cleavage | None |
| Fracture | Conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 5–6 |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Transparent |
| Density | 2.76 (measured) |
| Optical properties | Uniaxial (+) |
| Refractive index | nω = 1.62, nε = 1.63 (approximated) |
| Pleochroism | Colorless to pink (W), pink (E) |
| Ultraviolet fluorescence | Orange-red |
| Common impurities | Sr, REE, K, Ba, Zr |
| References | |
Alluaivite is a rare mineral of the eudialyte group, with complex formula written as Na19(Ca,Mn)6(Ti,Nb)3Si26O74Cl·2H2O. It is unique among the eudialyte group as the only titanosilicate (other representatives of the group are usually zirconosilicates). The two dual-nature minerals of the group, being both titano- and zirconosilicates, are labyrinthite and dualite. They both contain alluaivite module in their structures. Alluaivite is named after Mt. Alluaiv in Lovozero Tundry massif, Kola Peninsula, Russia, where it is found in ultra-agpaitic, hyperalkaline pegmatites.