Johnsenite-(Ce)
Johnsenite-(Ce) is a very rare mineral of the eudialyte group,[1] with the chemical formula Na
12(Ce,La,Sr,Ca,[ ])
3Ca
6Mn
3Zr
3WSi(Si
9O
27)
2(Si
3O
9)
2(CO
3)O(OH,Cl)
2.[2] 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.[3] It is the third eudialyte-group mineral with essential tungsten (after khomyakovite and manganokhomyakovite), and second with essential rare earth elements (after zirsilite-(Ce),[1] which is the niobium-analogue of johnsenite-(Ce)). In fact, some niobium substitutes for tungsten in johnsenite-(Ce).[2] Other characteristic feature is the presence of essential carbonate group, shared with carbokentbrooksite, golyshevite, mogovidite and zirsilite-(Ce).[1]
| Johnsenite-(Ce) | |
|---|---|
| General | |
| Category | Cyclosilicate |
| Formula (repeating unit) | Na 12(Ce,La,Sr,Ca,[ ]) 3Ca 6Mn 3Zr 3WSi(Si 9O 27) 2(Si 3O 9) 2(CO 3)O(OH,Cl) 2 (original form) |
| 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 | [1][2] |
Occurrence and association
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.[4] 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).[2]
Notes on chemistry
Notable impurities in johnsenite-(Ce) are iron, titanium, niobium, yttrium, potassium, praseodymium, and neodymium. Traces of gadolinium, samarium, and hafnium are also reported.[2]
Notes on crystal structure
Johnsenite-(Ce) has four-layer structure.[2]
References
- Mindat, Johnsenite-(Ce), http://www.mindat.org/min-27479.html
- Grice, J.D., and Gault, R.A., 2006. Johnsenite-(Ce): a new member of the eudialyte group from Mont-Saint Hilaire, Quebec, Canada. The Canadian Mineralogist 44, 105-115
- Johnsen, O., Ferraris, G., Gault, R.A., Grice, D.G., Kampf, A.R., and Pekov, I.V., 2003. The nomenclature of eudialyte-group minerals. The Canadian Mineralogist 41, 785-794
- "Poudrette quarry (Demix quarry; Uni-Mix quarry; Desourdy quarry; Carrière Mont Saint-Hilaire), Mont Saint-Hilaire, La Vallée-du-Richelieu RCM, Montérégie, Québec, Canada - Mindat.org". Mindat.org. Retrieved 2016-03-11.