osmium

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Hard, heavy, bluish-white, metallic element, atomic number 76, relative atomic mass 190.2. Together with the elements ruthenium, rhodium, palladium, iridium, and platinum, it forms the group of platinum metals, which have similar physical and chemical properties. It is resistant to tarnish and corrosion. It occurs in platinum ores and as a free metal (see native metal) with iridium in a natural alloy called osmiridium, containing traces of the other platinum group metals. Its uses include pen points and light-bulb filaments; like platinum, it is a useful catalyst.

It was discovered in 1803 and named in 1804 by English chemist Smithson Tennant (1761–1815) after the irritating smell of one of its oxides.

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