Discovery of iridium

Iridium was discovered in 1803 by the English chemist Smithson Tennant in London. He was studying the black residue that remained when crude platinum was dissolved in aqua regia, and found that it contained not graphite, as many believed, but two new metals, iridium and osmium. Iridium was named after Iris, the Greek goddess of the rainbow, because its salts show a wide range of colours. It is one of the densest and most corrosion-resistant elements and is very rare in the Earth's crust, but more common in meteorites. In 1980 Luis and Walter Alvarez and their colleagues found an unusual layer of iridium at the boundary between the Cretaceous and Paleogene periods, which became key evidence that an asteroid impact helped cause the extinction of the dinosaurs.

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