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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.
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| 1. From Yttria |
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| 2. From Ceria |
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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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