As defined by IUPAC, rare earth elements ("REEs") or rare earth metals are a set of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides plus scandium and yttrium. Scandium and yttrium are considered rare earth elements since they tend to occur in the same ore deposits as the lanthanides and exhibit similar chemical properties.
Despite their name, rare earth elements (with the exception of the radioactive promethium) are relatively plentiful in the Earth's crust. However, because of their geochemical properties, rare earth elements are typically dispersed and not often found in concentrated and economically exploitable forms
Historically, rare earth elements were synonymous with the 15 lanthanides. (need reference)
Some definitions of REEs also include thorium (Cf. AGI Glossary of Geology, 4th Edition).
Geological keywords, such as “granite”, “lake”. The definitions are generally taken from the AGI Glossary of Geology. Keywords with a geographic context (e.g. Cape Smith Fold Belt, Selwyn Basin, Grenville Province) are assigned to a separate category.
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