Iridium is a chemical element with the symbol Ir and atomic number 77. A very hard, brittle, silvery-white transition metal of the platinum group, iridium is considered to be the second-densest naturally occurring metal with a density of 22.56 g/cm³ as defined by experimental X-ray crystallography.

How was iridium discovered?

Iridium was discovered together with osmium in1803 by Smithson Tennant in London. When crude platinum was dissolved in dilute aqua regia, which is a mixture of nitric and hydrochloric acids, it left behind a black residue thought to be graphite.

When was iridium formed?

Iridium was discovered in 1803, by English chemist Smithson Tennant in London. He found it in the residue left when crude platinum had been dissolved in aqua regia (a mixture of hydrochloric acid and nitric acid). Smithson Tennant also discovered osmium at the same time.