Johnsenite-(Ce)
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8/E.25-57 (8 ed)
| Johnsenite-(Ce) | |
|---|---|
| General | |
| Category | Cyclosilicate |
| Formula | Na12(Ce,La,Sr,Ca,[ ])3Ca6Mn3Zr3WSi(Si9O27)2(Si3O9)2(CO3)O(OH,Cl)2 (original form) |
| IMA symbol | Jsn[1] |
| Strunz classification | 9.CO.10 (10 ed) 8/E.25-57 (8 ed) |
| Dana classification | 64.1.2.7 |
| Crystal system | Trigonal |
| Crystal class | Hexagonal scalenohedral (3m) H-M symbol: (3 2m) |
| Space group | R3m |
| Unit cell | a = 14.24, c = 30.03 [Å] (approximated); Z = 3 |
| Identification | |
| Color | Pale yellow to bright orange |
| Crystal habit | Skeletal crystals (etched); aggregates |
| Cleavage | None |
| Fracture | Uneven |
| Tenacity | Brittle |
| Mohs scale hardness | 5–6 |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Transparent or translucent |
| Density | 3.24 (measured) |
| Optical properties | Uniaxial (−) |
| Refractive index | nω = 1.65, nε = 1.64 (approximated) |
| Pleochroism | None |
| References | [2][3] |
Johnsenite-(Ce) is a very rare mineral of the eudialyte group,[2] with the chemical formula Na12(Ce,La,Sr,Ca,[ ])3Ca6Mn3Zr3WSi(Si9O27)2(Si3O9)2(CO3)O(OH,Cl)2.[3] The original formula was extended to show the presence of both the cyclic silicate groups and silicon at the M4 site, according to the nomenclature of the eudialyte group.[4] It is the third eudialyte-group mineral with essential tungsten (after khomyakovite and manganokhomyakovite), and second with essential rare earth elements (after zirsilite-(Ce),[2] which is the niobium-analogue of johnsenite-(Ce)). In fact, some niobium substitutes for tungsten in johnsenite-(Ce).[3] Other characteristic feature is the presence of essential carbonate group, shared with carbokentbrooksite, golyshevite, mogovidite and zirsilite-(Ce).[2]
Johnsenite-(Ce) was discovered in alkaline rocks of Mont Saint-Hilaire, Quebec, Canada, which is also a type locality for other eudialyte group species: oneillite, khomyakovite and manganokhomyakovite.[5] The association of johnsenite-(Ce) is rich, as it includes aegirine, albite, amphibole-group mineral, burbankite-group mineral, calcite, catapleiite, cerite-(Ce), dawsonite, epididymite, fluorapophyllite, galena, microcline, molybdenite, natrolite, pectolite, pyrite, pyrrhotite, quartz, rhodochrosite, sphalerite, steacyite, stillwellite-(Ce), titanite, tuperssuatsiaite, zakharovite and zirsilite-(Ce).[3]
