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The Rare Earth Metals
Note: Promethium (Pm) does not occur naturally in the Earth's crust. It is a radio active element that has only been made artificially as a product of uranium fission.
The rare earth metals are so called because they were identified from mineral samples from two specific areas, Ytterby quarry, near Stockholm, Sweden and Bastnäs Mine, Sweden. It took scientists a long time to identify all of the rare earth metals (1803 - 1907). This is because the rare earth metals have very similar chemical properties and they are very closely associated with each other in the two mineral samples. The word "earth" is a name once used to describe the oxide of metals. The mineral samples from Ytterby and Bastnäs contained complex metal oxide compounds. These represented, between the two samples, all of the rare earth metals.
During the one hundred year period that the two minerals were investigated there were many claims that a new metal had been identified that were later proved false. In fact, the so-called new metal had been a mixture of compounds containing two or more separate new metals. The advancement of spectroscopy and Dmitri Mendeleev's periodic table helped to sort out the confusion.
The diagrams below indicate how the rare earth elements were identified.
1. From Yttria
2. From Ceria
All rare earth metals are silvery-white or grey. They tend to be shiny but soft and easily cut with a knife. They are not found as their pure elements in the Earth's crust because they are too reactive. They occur together in forms of minerals called monazite (found in the USA, Brazil and Australia) and bastnasite (found in Sweden and California, USA). The rare earth metals are not themselves rare; in fact, some of them are more abundant than zinc and lead in the Earth's crust.
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