Johnsenite-(Ce)
Johnsenite-(Ce) is a very rare mineral of the eudialyte group, with the chemical 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)).
Intro adapted from Wikipedia (CC BY-SA).
Johnsenite-(Ce) is an IMA-recognized mineral species in the silicate class, with the chemical formula Na₁₂Ce₃Ca₆Mn₃Zr₃WSi₂₅O₇₃(CO₃)(OH)₂.
It crystallizes in the hexagonal crystal system (space group R3m). It is a member of the Eudialyte structural group.
Key properties: Mohs hardness 5–6; specific gravity 3.24; White streak; Vitreous luster; optically uniaxial.
IMA symbol Jsn-Ce, IMA status: approved, named in 2004.
Found in a cavity near the margin of a marble xenolith in an igneous breccia along the contact between porphyritic nepheline syenite and sodalite syenite in an alkaline igneous complex.
It is found associated with Albite, calcite, pectolite, aegirine, fluorapophyllite, zirsilite-(Ce), a burbankite group mineral, dawsonite, rhodochrosite, epididymite, galena, molybdenite.
The mineral was named to honor Ole Johnsen (b. 1940), Geological Museum, University of Copenhagen, Denmark, for his research on the eudialyte group and the minerals of Greenland.