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. 1 2 3 4 5 Mindat, http://www.mindat.org/min-26453.html
  2. 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
  3. 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
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