Johnsenite-(Ce)

Johnsenite-(Ce)
General
Category Silicate mineral, Cyclosilicate
Formula
(repeating unit)
Na12(Ce,La,Sr,Ca,[])3Ca6Mn3Zr3WSi25O73)(CO3)O(OH,Cl)2 (original form)
Strunz classification 8/E.25-57
Dana classification 64.1.2.7
Crystal system Trigonal, R3m'
Unit cell a=14.24, c=30.03 [Å] (approximated)
Identification
Color Pale yellow to bright orange
Crystal habit skeletal crystals (etched); aggregates
Crystal symmetry Trigonal - Ditrigonal Pyramidal (3m)
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]

Johnsenite-(Ce) is a very rare mineral of the eudialyte group,[1] with formula Na12(Ce,La,Sr,Ca,[])3Ca6Mn3Zr3WSi(Si9O27)2(Si3O9)2(CO3)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]

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

  1. 1 2 3 4 Mindat, Johnsenite-(Ce), http://www.mindat.org/min-27479.html
  2. 1 2 3 4 5 6 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
  3. 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
  4. "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.
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