Carbokentbrooksite
From Wikipedia, the free encyclopedia
8/E.25-32 (8 ed)
| Carbokentbrooksite | |
|---|---|
| General | |
| Category | Silicate mineral, Cyclosilicate |
| Formula | (Na,□)12(Na,Ce)3Ca6Mn3Zr3Nb(Si25O73)(OH)3(CO3)·H2O (original form) |
| IMA symbol | Cktb[1] |
| Strunz classification | 9.CO.10 (10 ed) 8/E.25-32 (8 ed) |
| Dana classification | 64.1.2.3 |
| Crystal system | Trigonal |
| Crystal class | Ditrigonal pyramidal (3m) (same H-M symbol) |
| Space group | R3m |
| Unit cell | a = 14.24, c = 30.04 [Å]; Z = 3 |
| Identification | |
| Color | Yellow, yellow-orange |
| Crystal habit | rhombohedra (cores of zoned crystals) |
| Cleavage | None |
| Fracture | Conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 5 |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Transparent |
| Density | 3.14 (measured) |
| Optical properties | Uniaxial (−) |
| Refractive index | nω = 1.65, nε = 1.64 (approximated) |
| Pleochroism | None |
| Ultraviolet fluorescence | No |
| References | [2][3] |
Carbokentbrooksite is a very rare mineral of the eudialyte group,[2] with formula (Na,□)12(Na,Ce)3Ca6Mn3Zr3NbSiO(Si9O27)2(Si3O9)2(OH)3(CO3).H2O.[3] The original formula was extended to show the presence of cyclic silicate groups and silicon at the M4 site, according to the nomenclature of eudialyte group.[4] Carbokenbrooksite characterizes in being carbonate-rich (the other eudialyte-group species with essential carbonate are zirsilite-(Ce), golyshevite, and mogovidite). It is also sodium rich, being sodium equivalent of zirsilite-(Ce),[2] with which it is intimately associated.[3]
Carbokentbrooksite and zirsilite-(Ce) are found as replacements of grains and crystals of eudialyte.[2] They occur in pegmatites of Darai-Pioz alkaline massif, Tajikistan – a locality known for many rare minerals.[5] The minerals are associated with aegirine, ekanite, microcline, polylithionite, quartz, stillwellite-(Ce) (silicates), pyrochlore-group mineral, fluorite, calcite, and galena.[3]
