Zirsilite-(Ce) | |
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General | |
Category | Cyclosilicate |
Formula (repeating unit) | (Na,□)12(Ce,Na)3Ca6Mn3Zr3Nb(Si25O73)(OH)3(CO3)·H2O (original form) |
IMA symbol | Zir-Ce [1] |
Strunz classification | 9.CO.10 |
Dana classification | 64.1.5 |
Crystal system | Trigonal |
Crystal class | Ditrigonal pyramidal (3m) H-M symbol: (3m) |
Space group | R3m |
Unit cell | a = 14.25, c = 30.08 [Å] (approximated); Z = 3 |
Identification | |
Color | Creamy white |
Crystal habit | rhombohedra (rims of zoned crystals) |
Cleavage | None |
Fracture | Conchoidal |
Tenacity | Brittle |
Mohs scale hardness | 5 |
Luster | Vitreous |
Streak | White |
Diaphaneity | Transparent |
Density | 3.15 (measured) |
Optical properties | Uniaxial (−) |
Refractive index | nω = 1.65, nε = 1.64 (approximated) |
Pleochroism | None |
Ultraviolet fluorescence | No |
References | [2] [3] |
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] [3] 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. [4] Zirsilite-(Ce) differs from carbokentbrooksite in cerium-dominance over sodium only. Both minerals are intimately associated. [2] [3] 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 [5]) in dominance is johnsenite-(Ce). [2]
Zirsilite-(Ce) and carbokentbrooksite occur in pegmatites of Darai-Pioz alkaline massif, Tajikistan – a locality known for many rare minerals. [6] They are found as replacements of grains and crystals of eudialyte. [2] The minerals are associated with aegirine, ekanite, microcline, polylithionite, quartz, stillwellite-(Ce) (silicates), pyrochlore-group mineral, fluorite, calcite, and galena. [3]
Beside the elements given in the formula, zirsilite-(Ce) contains admixtures of lanthanum, strontium, neodymium, iron, yttrium, titanium, potassium, chlorine, and praseodymium. [3]
Zirsilite-(Ce) is isostructural with kentbrooksite. [3]