Johnsenite-(Ce)

Johnsenite-(Ce) is a very rare mineral of the eudialyte group,[1] with the chemical formula Na
12
(Ce,La,Sr,Ca,[ ])
3
Ca
6
Mn
3
Zr
3
WSi(Si
9
O
27
)
2
(Si
3
O
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
CategoryCyclosilicate
Formula
(repeating unit)
Na
12
(Ce,La,Sr,Ca,[ ])
3
Ca
6
Mn
3
Zr
3
WSi(Si
9
O
27
)
2
(Si
3
O
9
)
2
(CO
3
)O(OH,Cl)
2
(original form)
Strunz classification9.CO.10 (10 ed)
8/E.25-57 (8 ed)
Dana classification64.1.2.7
Crystal systemTrigonal
Crystal classHexagonal scalenohedral (3m)
H-M symbol: (3 2m)
Space groupR3m
Unit cella = 14.24, c = 30.03 [Å] (approximated); Z = 3
Identification
ColorPale yellow to bright orange
Crystal habitskeletal crystals (etched); aggregates
CleavageNone
FractureUneven
TenacityBrittle
Mohs scale hardness5-6
LusterVitreous
StreakWhite
DiaphaneityTransparent or Translucent
Density3.24 (measured)
Optical propertiesUniaxial (-)
Refractive indexnω=1.65, nε=1.64 (approximated)
PleochroismNone
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

  1. Mindat, Johnsenite-(Ce), http://www.mindat.org/min-27479.html
  2. 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.
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.