The rare earths are not “rare” in the commonly used sense of the word; the term derives from an old form of the word rare, meaning “difficult”. In fact the 17 rare earths - the 15 lanthanides plus scandium and yttrium - are relatively abundant, with the most common rare earth, cerium, being as plentiful as copper in the earth's crust.It is this difficulty in extracting and separating the rare earths that led to their relatively late discovery and application.
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