Iridium was discovered in 1803 among insoluble impurities in natural platinum. Although only certain molten salts and halogens are corrosive to solid iridium, finely divided iridium dust is much more reactive and can be flammable. It is the most corrosion-resistant metal, even at temperatures as high as 2000 ☌. Still, the experimental X-ray crystallography value is considered to be the most accurate, and as such iridium is considered to be the second densest element. However, at room temperature and standard atmospheric pressure, iridium has been calculated to have a density of 22.65 g/cm 3, 0.04 g/cm 3 higher than osmium measured the same way. A very hard, brittle, silvery-white transition metal of the platinum group, iridium is considered to be the second-densest naturally occurring metal (after osmium) with a density of 22.56 g/cm 3 as defined by experimental X-ray crystallography. Iridium is a chemical element with the symbol Ir and atomic number 77.
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