Any of a group of chemically similar metallic elements comprising the lanthanide series and (usually) scandium and yttrium. They are not especially rare, but they tend to occur together in nature and are difficult to separate from one another.
- ‘Thulium is a rare earth element, one of the elements found in row 6 of the periodic table.’
- ‘Dysprosium is one of 15 rare earth elements, a family also known as the lanthanides.’
- ‘The effect was predicted to be very weak, but least weak with rare earth and transition metal ions.’
- ‘It occurs primarily with the other rare earth elements in two minerals, monazite and bastnasite.’
- ‘The members of this family are also known as the rare earth elements.’