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Precious metal
dangerous because it emits radiation that is absorbed by bone marrow, one of the results of which can be leukemia.
(See also: Americium.) Polonium (Po)
Element 84 on the periodic table. A radioactive, silvery-grey metal of group 6 (the oxygen group).
It was the first radioactive element to be discovered, in 1898 by Pierre and Marie Curie. Polonium is very rare.
Praseodymium (Pr)
Element 59 on the periodic table. This silvery-coloured, soft metal is one of the rare-earth metals and
a lanthanide.
Discovered in 1885 by Carl Auer von Welsbach, it is used as an alloy in high-strength metals.
Precious metal
The elements gold (Au), iridium (Ir), osmium (Os), palladium (Pd), platinum (Pt), rhodium (Rh), ruthenium (Ru) and silver
(Ag). All of these metals have similar properties and occur in adjacent positions on the periodic table as well as being found together in nature.
The precious metals are very rare and are found in amounts equal to less than one part per million in
the Earth’s crust. However, many metals are very rare. A precious metal is not only rare, but also belongs to the group of noble metals – the most unreactive of all the metals.
Potassium (K)
Element 19 on the periodic table. A soft, white, reactive metal and an element of group 1 (the alkali metals).
It is found in all living matter. The pure metal, however, has little direct use.
Potassium was discovered
in 1807 by the English
chemist Sir Humphry Davy.
 Potassium – Potassium is a reactive metal. Here it burns on the surface of water.
 Potassium – Potassium is a vital element in
giving some minerals
their character.
Muscovite, for
example, is
potassium
aluminium silicate.
It differs from many other minerals based
on aluminium and silicon by the presence of the potassium.
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