We don't have synonyms for rare earths yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are rare earth.
(n) :
(chemistry) Any of the naturally occurring oxides of the lanthanide metals; they are widely distributed in relatively small concentrations and are used in glassmaking, ceramic glazes etc.
(n) :
(chemistry) Any of the naturally occurring oxides of the lanthanide metals; they are widely distributed in relatively small concentrations and are used in glassmaking, ceramic glazes etc.