stillwellite-(Ce)

{{infobox mineral | name = Stillwellite-(Ce) | category = Silicate mineral | boxwidth = | boxbgcolor = | image = Stillwellite-(Ce)-33971.jpg | imagesize = | alt = | caption = 1.3 cm stillwellite-(Ce) crystal in matrix | formula = | IMAsymbol = Swl | molweight = | strunz = 9.AJ.25 | dana = 54.02.03.02 | system = Trigonal | class = Pyramidal (3) H-M symbol: (3) | symmetry = P31 | color = Red-brown to pale pink | colour = | habit = Flat rhombohedral crystals, massive | twinning = Observed on {100} | cleavage = Imperfect | fracture = Conchoidal | tenacity = | mohs = 6.5 | luster = Resinous | streak = White | diaphaneity = Transparent to translucent | gravity = 4.57–4.6 | density = | polish = | opticalprop = Uniaxial (+) | refractive = nω = 1.765, nε = 1.780 | birefringence = δ = 0.015 | pleochroism = | 2V = | dispersion = | extinction = | length fast/slow = | fluorescence= | absorption = | melt = | fusibility = | diagnostic = | solubility = | other = 25px Radioactive | alteration = | references = }} Stillwellite-(Ce) is a rare-earth boro-silicate mineral with chemical formula .

== Location == It occurs as a metasomatic replacement of metamorphosed limestones in the Mary Kathleen mine, Australia and in alkalic pegmatites associated with syenite in an alkaline massif in Tajikistan. It occurs in association with allanite, garnet, uraninite in the Australian deposit; with calcite, monazite, bastnasite, thorite, uranothorite and thorianite in the Desmont mine, Wilberforce, Ontario, Canada; and with pyrochlore, tienshanite, sogdianite, thorite, caesium kupletskite, reedmergnerite, steacyite, pectolite and quartz in the Tajikistan deposit. It has also been reported from Mont Saint-Hilaire, Quebec, Canada and from Mineville, Essex County, New York. Other occurrences include the Inagli massif, Yakutia, Russia, around Langesundsfjord, Norway, in the Ilimaussaq intrusive complex, southern Greenland and the Vico volcano, Lazio, Italy.