Zirsilite-(Ce)

Zirsilite-(Ce) is a very rare mineral of the eudialyte group, with formula (Na,[])12(Ce,Na)3Ca6Mn3Zr3NbSi(Si9O27)2(Si3O9)2O(OH)3(CO3)•H2O.[2][1] The original formula was extended to show the presence of cyclic silicate groups and the presence of silicon at the M4 site, according to the nomenclature of the eudialyte group.according to the nomenclature of eudialyte group.[3] Zirsilite-(Ce) differs from carbokentbrooksite in cerium-dominance over sodium only. Both minerals are intimately associated.[1][2] The only other currently known representative of the eudialyte group having rare earth elements (in particular cerium, as suggested by the "-Ce)" Levinson suffix in the name[4]) in dominance is johnsenite-(Ce).[1]

Zirsilite-(Ce)
General
CategoryCyclosilicate
Formula
(repeating unit)		(Na,□)12(Ce,Na)3Ca6Mn3Zr3Nb(Si25O73)(OH)3(CO3)•H2O (original form)
Strunz classification9.CO.10
Dana classification64.1.5
Crystal systemTrigonal
Crystal classDitrigonal pyramidal (3m)
H-M symbol: (3m)
Space groupR3m
Unit cella = 14.25, c = 30.08 [Å] (approximated); Z = 3
Identification
ColorCreamy white
Crystal habitrhombohedra (rims of zoned crystals)
CleavageNone
FractureConchoidal
TenacityBrittle
Mohs scale hardness5
LusterVitreous
StreakWhite
DiaphaneityTransparent
Density3.15 (measured)
Optical propertiesUniaxial (-)
Refractive indexnω=1.65, nε=1.64 (approximated)
PleochroismNone
Ultraviolet fluorescenceNo
References[1][2]

Occurrence and association

Zirsilite-(Ce) and carbokentbrooksite occur in pegmatites of Darai-Pioz alkaline massif, Tajikistan - a locality known for many rare minerals.[5] They are found as replacements of grains and crystals of eudialyte.[1] The minerals are associated with aegirine, ekanite, microcline, polylithionite, quartz, stillwellite-(Ce) (silicates), pyrochlore-group mineral, fluorite, calcite, and galena.[2]

Notes on chemistry

Beside the elements given in the formula, zirsilite-(Ce) contains admixtures of lanthanum, strontium, neodymium, iron, yttrium, titanium, potassium, chlorine, and praseodymium.[2]

Notes on structure

Zirsilite-(Ce) is isostructural with kentbrooksite.[2]

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References
  1. Mindat, Zirsilite-(Ce), http://www.mindat.org/min-25674.html
  2. Khomyakov, A.P., Dusmatov, V.D., Ferraris, G., Gula, A., Ivaldi, G., and Nechelyustov, G.N., 2003: Zirsilite-(Ce), (Na,□)12(Ce,Na)3Ca6Mn3Zr3Nb(Si25O73)(OH)3(CO3)•H2O, and carbokentbrooksite (Na,□)12(Na,Ce)3Ca6Mn3Zr3Nb(Si25O73)(OH)3(CO3)•H2O - two new eudialyte-group minerals from the Dara-i-Pioz alkaline massif, Tajikistan. Zapiski Vserossiyskogo Mineralogicheskogo Obshchestva 132(5), 40–51 (in Russian, with English abstract); in: Jambor, J.I, and Roberts, A.C., 2004: New mineral names. American Mineralogist 89(11-12), 1826-1834
  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
  4. Hatert, F., Mills, S.J., Pasero, M., and Williams, P.A., 2013. CNMNC guidelines for the use of suffixes and prefixes in mineral nomenclature, and for the preservation of historical names. European Journal of Mineralogy 25, 113-115
  5. "Darai-Pioz Glacier (Dara-i-Pioz; Dara-Pioz), Alai Range (Alayskiy), Tien Shan Mtn, Region of Republican Subordination, Tajikistan - Mindat.org". Mindat.org. Retrieved 2016-03-11.
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