The substances occur, in very minute quantity, in a large number of sparingly-distributed and comparatively rare minerals - euxenite, samarksite, cerite, yttrotantalite, &c. Scandinavian specimens of these minerals were examined by J.
Hisinger and Berzelius, was of ceria, the oxide of cerium, in the mineral cerite found at Ridderhytta, Westmannland, Sweden.
In 1841 Mosander, having in 1839 discovered a new element lanthanum in the mineral cerite, isolated this element and also a hitherto unrecognized substance, didymia, from crude yttria, and two years later he announced the determination of two fresh constituents of the same earth, naming them erbia and terbia.
Mosander from cerite (1839-1841).
It is found in the minerals gadolinite, cerite, samarskite and fergusonite, and is usually obtained from cerite.