Zirsilite-(Ce)
Rare mineral of the eudialyte group
From Wikipedia, the free encyclopedia
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]
-830936.jpg)
| Zirsilite-(Ce) | |
|---|---|
| |
| General | |
| Category | Cyclosilicate |
| Formula | (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] |
Occurrence and association
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]
Notes on chemistry
Notes on structure
Zirsilite-(Ce) is isostructural with kentbrooksite.[3]