Iridium

Iridium is a chemical element; it has the symbol Ir and atomic number 77. This very hard, brittle, silvery-white transition metal of the platinum group is considered the second-densest naturally occurring metal (after osmium), with a density of as defined by experimental X-ray crystallography. 191Ir and 193Ir are the only two naturally occurring isotopes of iridium, as well as the only stable isotopes; the latter is the more abundant. It is one of the most corrosion-resistant metals, even at temperatures as high as .

British chemist (1761-1815)

isotopes of iridium

thin layer of the element iridium in rock strata at the Cretaceous–Paleogene boundary

alloys of the precious metals platinum and iridium