Any of a large class of chemical elements including scandium (atomic number 21), yttrium (39), and the 15 elements from 57 (lanthanum) to 71 (see lanthanides). The rare earths themselves are pure or mixed oxides of these metals, originally thought to be quite scarce; however, cerium, the most plentiful, is three times as abundant as lead in the Earth's crust. The metals never occur free, and the pure oxides never occur in minerals. These metals are similar chemically because their atomic structures are generally similar; all form compounds in which they have valence 3, including stable oxides, carbides, and borides.
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It can also refer to:
RARE DISEASES DAY: SURVEY SHOWS STRONG PUBLIC SUPPORT FOR EUROPEAN COOPERATION ON RARE DISEASES.(Disease/ Disorder overview)
Feb 28, 2011; BRUSSELS -- The following information was released by the European Union: RARE diseases cause great suffering to many EU...