Johnsenite-(Ce)

{{Short description|Mineral of the eudialyte group}}

{{infobox mineral

| name = Johnsenite-(Ce)

| category = Cyclosilicate

| image =

| imagesize =

| alt =

| caption =

| formula = {{chem2|Na12(Ce,La,Sr,Ca,[ ])3Ca6Mn3Zr3WSi(Si9O27)2(Si3O9)2(CO3)O(OH,Cl)2}} (original form)

| IMAsymbol = Jsn{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}

| strunz = 9.CO.10 (10 ed)
8/E.25-57 (8 ed)

| dana = 64.1.2.7

| system = Trigonal

| class = Hexagonal scalenohedral ({{overline|3}}m)
H-M symbol: ({{overline|3}} 2m)

| symmetry = R{{overline|3}}m

| unit cell = a = 14.24, c = 30.03 [Å] (approximated); Z = 3

| color = Pale yellow to bright orange

| colour =

| habit = Skeletal crystals (etched); aggregates

| twinning =

| cleavage = None

| fracture = Uneven

| tenacity = Brittle

| mohs = 5–6

| luster = Vitreous

| streak = White

| diaphaneity = Transparent or translucent

| gravity =

| density = 3.24 (measured)

| polish =

| opticalprop = Uniaxial (−)

| refractive = nω = 1.65, nε = 1.64 (approximated)

| birefringence =

| pleochroism = None

| 2V =

| dispersion =

| extinction =

| length fast/slow =

| fluorescence =

| absorption =

| melt =

| fusibility =

| diagnostic =

| solubility =

| impurities =

| alteration =

| other =

| references =

}}

Johnsenite-(Ce) is a very rare mineral of the eudialyte group,Mindat, Johnsenite-(Ce), http://www.mindat.org/min-27479.html with the chemical formula {{chem2|Na12(Ce,La,Sr,Ca,[ ])3Ca6Mn3Zr3WSi(Si9O27)2(Si3O9)2(CO3)O(OH,Cl)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 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.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 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).