Noun
A rare earth, regarded by some as an oxide of the supposed element gadolinium, by others as only a mixture of the oxides of yttrium, erbium, ytterbium, etc.
Source: Webster's dictionaryBecause he realized that "gadolinia" was the oxide of a new element, he is credited with discovery of gadolinium. Source: Internet
French chemist Paul Émile Lecoq de Boisbaudran actually carried out the separation of gadolinium metal from gadolinia, in 1886. Source: Internet