| Na12(Ce,La,Sr,Ca,)3Ca6Mn3Zr3WSi25O73)(CO3)O(OH,Cl)2 (original form)|
9.CO.10 (10 ed)
8/E.25-57 (8 ed)
Hexagonal scalenohedral (3m)
H-M symbol: (3 2m)
Johnsenite-(Ce) is a very rare mineral of the eudialyte group, with formula Na12(Ce,La,Sr,Ca,)3Ca6Mn3Zr3WSi(Si9O27)2(Si3O9)2(CO3)O(OH,Cl)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. It is the third eudialyte-group mineral with essential tungsten (after khomyakovite and manganokhomyakovite), and second with essential rare earth elements (after zirsilite-(Ce), which is the niobium-analogue of johnsenite-(Ce)). In fact, some niobium substitutes for tungsten in johnsenite-(Ce). Other characteristic feature is the presence of essential carbonate group, shared with carbokentbrooksite, golyshevite, mogovidite and zirsilite-(Ce).
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. 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).