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.
The rare earth metals are found in the minerals gadolinite, samarskite, fergusonite, euxenite and cerite.
It is usually found associated with tantalum, the chief minerals containing these two elements being tantalite, columbite, fergusonite and yttrotantalite; it is also a constituent of pyrochlor, euxenite and samarskite.
Ilmenite is isomorphous with geikielite, MgTiO 3, and pyrophanite, MnTiO 3; many of the "rare minerals" - aeschynite, euxenite, polycrase, &c. - contain titanates (and also niobates).
CERIUM (symbol Ce, atomic weight 140.25), a metallic chemical element which occurs with the rare earths in the minerals cerite, samarskite, euxenite, monazite, parisite and many yttrium minerals.