A monoclinic mineral, (Na,Ca,Ce)₃Ti(Si₂O₇)₂OF₃; weakly radioactive; forms prismatic crystals in veins containing silicates of cerium metals, yttrium, and niobium; near Barkevik, Norway, in sodalite syenite in the Julianehaab district, Greenland, and in large crystals on the Kola Peninsula, Russia. Also spelled rinkolite.