Habit: Wax or honey yellow or reddish brown. Commonly tabular to equant crystals, horizontally striated, but may be elongated, or in syntaxic intergrowth with röntgenite-(Ce), synchysite-(Ce), parisite-(Ce) or cordylite-(Ce); also granular or massive. Vitreous to greasy luster, pearly on basal partings; transparent to translucent. White streak.
Environment: Typically hydrothermal, though primary igneous occurrences are known. Found in granite and alkali syenites and pegmatites, carbonatites and contact metamorphic deposits; rarely as detrital mineral in placers.
Etymology: Named for its first noted occurrence, in the Bastnäs Mine in Sweden.