Fluocerite, also known as tysonite, is a mineral consisting of cerium and lanthanum fluorides, with the chemical formula . The end members are classified as two different mineral types depending on the cation, fluocerite-(Ce) and fluocerite-(La), corresponding respectively to lanthanum trifluoride and cerium trifluoride. Both crystallize in the trigonal system.
Fluocerite-(Ce) was first described (without the Ce) in 1845 from hydrothermal veins in granite in Sweden. Fluocerite-(La) was first described in 1969 from the type locality in central Kazakhstan. The name tysonite was given in 1880 to the same type of mineral found in Colorado.Allen, Oscar D., and W. J. Comstock. "Bastnaesite and tysonite from Colorado." American Journal of Science 3.113 (1880): 390-393. Tysonite-type structure is used for rare-earth fluorides with the P3c1 space group structure.
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