| Zirsilite-(Ce) | |
| Category: | Cyclosilicate |
| Formula: | (original form) |
| Imasymbol: | Zir-Ce[1] |
| Strunz: | 9.CO.10 |
| Dana: | 64.1.5 |
| Class: | Ditrigonal pyramidal (3m) H-M symbol: (3m) |
| Symmetry: | R3m |
| Unit Cell: | a = 14.25, c = 30.08 [Å] (approximated); Z = 3 |
| Color: | Creamy white |
| Habit: | rhombohedra (rims of zoned crystals) |
| Cleavage: | None |
| Fracture: | Conchoidal |
| Tenacity: | Brittle |
| Mohs: | 5 |
| Luster: | Vitreous |
| Streak: | White |
| Diaphaneity: | Transparent |
| Density: | 3.15 (measured) |
| Opticalprop: | Uniaxial (−) |
| Refractive: | nω = 1.65, nε = 1.64 (approximated) |
| Pleochroism: | None |
| Fluorescence: | No |
Zirsilite-(Ce) is a very rare mineral of the eudialyte group, with formula .[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. 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).
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. The minerals are associated with aegirine, ekanite, microcline, polylithionite, quartz, stillwellite-(Ce) (silicates), pyrochlore-group mineral, fluorite, calcite, and galena.
Beside the elements given in the formula, zirsilite-(Ce) contains admixtures of lanthanum, strontium, neodymium, iron, yttrium, titanium, potassium, chlorine, and praseodymium.
Zirsilite-(Ce) is isostructural with kentbrooksite.