Raslakite
| Raslakite | |
|---|---|
Red glassy raslakite in nepheline-syenite from the type locality: Karnasurt Mountain, Lovozero Massif, Northern Region, Russian Federation. | |
| General | |
| Category | Silicate mineral |
| Formula | Na15Ca3Fe3(Na,Zr)3Zr3(Si,Nb)(Si25O73)(OH,H2O)3(Cl,OH) (original form) |
| IMA symbol | Rsk |
| Strunz classification | 9.CO.10 |
| Crystal system | Trigonal |
| Crystal class | Pyramidal (3) H-M symbol: (3) |
| Space group | R3 |
| Unit cell | a = 14.23, c = 30.02 [Å]; Z = 3 |
| Identification | |
| Color | Brownish-red |
| Crystal habit | Grains |
| Cleavage | Imperfect |
| Fracture | Conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 5 |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Transparent |
| Specific gravity | 2.95 (measured) |
| Optical properties | Uniaxial |
| Refractive index | nω = 1.61, nε = 1.61 (approximated) |
| References | |
Raslakite is a rare mineral of the eudialyte group with the chemical formula Na15Ca3Fe3(Na,Zr)3Zr3(Si,Nb)SiO(Si9O27)2(Si3O9)2(OH,H2O)3(Cl,OH). This formula is based on the original one, and is extended to show the presence of cyclic silicate groups. The additional silicon and oxygen shown in separation from the cyclic groups (in parentheses) are in fact connected with two 9-fold rings. The mineral has lowered symmetry (space group R3, instead of more specific for the group R3m one), similarly to some other eudialyte-group members: aqualite, labyrinthite, oneillite and voronkovite. The specific feature of raslakite is, among others, the presence of sodium and zirconium at the M2 site. Raslakite was named after Raslak Cirques located nearby the type locality.