Carl Axel Arrhenius was a Swedish military officer, amateur geologist, and chemist. He is best known for his discovery of the mineral ytterbite in 1787.

The rare-earth elements (REE), also called the rare-earth metals or rare earths or, in context, rare-earth oxides, and sometimes the lanthanides, are a set of 17 nearly indistinguishable lustrous silvery-white soft heavy metals. Compounds containing rare earths have diverse applications in electrical and electronic components, lasers, glass, magnetic materials, and industrial processes.