Taseqite
| Raslakite | |
|---|---|
| General | |
| Category | Silicate mineral, Cyclosilicate |
| Formula (repeating unit) | Na12Sr3Ca6Fe3Zr3NbSi25O73)(O,OH,H2O)3Cl2 (original form) |
| Strunz classification | 9.CO.10 |
| Crystal system | Trigonal |
| Unit cell | a= 14.28, c= 30.02 [Å]; Z = 3 |
| Identification | |
| Color | Dark- to yellowish-brown; lemon yellow |
| Crystal habit | Thin tablets |
| Crystal symmetry |
Trigonal - ditrigonal pyramidal H-M symbol (3m) Space group: R3m |
| Cleavage | {0001}, fair |
| Fracture | Conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 5.5 |
| Luster | Vitreous |
| Streak | Brownish-wite |
| Diaphaneity | Transparent |
| Density | 3.24 g/cm3 (measured) |
| Optical properties | Uniaxial |
| Refractive index | nω=1.64, nε=1.65 (approximated) |
| References | [1][2] |
Taseqite is a rare mineral[1] of the eudialyte group, with formula Na12Sr3Ca6Fe3Zr3NbSiO(Si9O27)2(Si3O9)2(O,OH,H2O)3Cl2.[2] [1] The formula given is derived from the original one and shows a separate silicon at the M4 site, basing on the nomenclature of the eudialyte group.[3] Taseqite, khomyakovite and manganokhomyakovite are three group representatives with species-defining strontium, although many other members display stronium diadochy.[1] Both stronium (N4Sr) and niobium (M3Nb) are essential in the crystal structure of taseqite.[2] When compared to khomyakovite, taseqite differs in niobium- and chlorine-dominance.[1]
Occurrence and association
Taseqite's type locality is the Taseq slope located in the Ilimaussaq complex, Greenland - hence its name. At the type locality taseqite occurs in albitite veins, together with aegirine, analcime, catapleiite, ferrobustamite, hemimorphite, pectolite (silicates); ancylite-(La), calcite, dolomite, strontianite (carbonates); fluorapatite, and sphalerite.[2]
Notes on chemistry
Admixtures in taseqite include potassium and manganese, with traces of yttrium, cerium, hafnium, tantalum, and tin.[2]
References
- 1 2 3 4 5 Mindat, http://www.mindat.org/min-26453.html
- 1 2 3 4 5 Petersen, O.V., Johnsen, O., Gault, R.A., Niedermayr, G., and Grice, J.D., 2004. Taseqite, a new member of the eudialyte group from the Ilimaussaq alkaline complex, South Greenland. Neues Jahrbuch für Mineralogie Monatshefte Jg. 2004(2), 83-96
- ↑ Johnsen, O., Ferraris, G., Gault, R.A., Grice, D.G., Kampf, A.R., and Pekov, I.V., 2003. The nomenclature of eudialyte-group minerals. The Canadian Mineralogist 41, 785-794