Rinkite

General Information: Chemical Formula:(Na,Ca)3(Ca,Ce)4Ti4(Si2O7)2(O,F)4 Composition:(Molecular Weight = 936.98 gm)Sodium 5.52 % NaCalcium 16.04 % CaCerium 14.95 % CeTitanium 20.44 % TiSilicon 11.99 % SiOxygen 29.03 % O Fluorine 2.03 % F  Empirical Formula: Na2.25Ca3.75CeTi4(Si2O7)2O3F Environment:Mineral in sodalite-syenite rocks. Locality:Julianehaab district, Greenland.Physical Properties: Cleavage:[100] Good Color:yellow, yellowish green, or brown. Density:3.5 Diaphaniety:Transparent to translucent Habits:Prismatic - Crystals Shaped like Slender Prisms (e.g. tourmaline)., Tabular - Form dimensions are thin in one direction., Hardness:5 - Apatite Luster:Vitreous (Glassy) Streak:yellow whiteMore details...

(Ca,Ce)4Na(Na,Ca)2Ti(Si2O7)2F2(O,F)2