Rare - But Common

The designahon rare is rather inappropriate. The RE metals are rare compared to the alkaline earth metals, calcium, magnesium and so on, but are not especially rare in general. Cerium, the RE metal with the highest mean content in earth crust is more common than copper. Thulium, the rarest RE metal (with the exception of promethium) is more common in the earth s crust than is silver. 

RE metals other than scandium are very similar and occur with each other in the crust From among the large number of minerals a few are mentioned with their formulas in Tables 17.2 and 17.3. 

Of these minerals mainly monazite and bastnaesite are mined. In fact monazite is an important yttrium raw material although yttrium is not part of the mineral formula. Monazite contains thorium and because of that is slightly radioactive. 

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