Iridium is a metallic element with the symbol Ir, atomic number 77, atomic weight 192.22. The element name comes from Latin and originally means "rainbow". Iridium has a content of one millionth in the Earth's crust and is often dispersed with platinum elements in various ores of alluvial and sand deposits.

In 1803, British chemist Smithsonian Tennant and French chemist Descoty discovered two new elements - osmium and iridium - from the black powder remaining at the bottom of the vessel when dissolving crude platinum in aqua regia. There are two isotopes in nature: iridium-191 and iridium-193. The artificial radioactive isotope 192Ir is obtained by stable element 191Ir being irradiated by neutrons. Decay release γ Radiation, with a half-life of 74.2d, commonly used in industrial testing.