Johnsenite-(Ce)

Johnsenite-(Ce)
General
Category	Cyclosilicate
Formula (repeating unit)	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]

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.[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]

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.[3]

Notes on crystal structure

Johnsenite-(Ce) has four-layer structure.[3]

References

1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
2. Mindat, Johnsenite-(Ce), http://www.mindat.org/min-27479.html
3. 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
4. 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
5. "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.