191Ir193Ir

191Ir and 193Ir are the two stable isotopes of the chemical element iridium (atomic number 77). In naturally occurring iridium, these two isotopes dominate the composition, with approximate abundances of about 37% for 191Ir and 63% for 193Ir, adding up to nearly 100% of the element. Because they are stable, neither isotope undergoes radioactive decay under ordinary conditions.

Iridium itself is a dense, corrosion-resistant metal in the platinum group. It is relatively rare in the Earth's crust and is often obtained as a byproduct of nickel and platinum group metal mining. The two stable isotopes arise from stellar nucleosynthesis, and their fixed natural abundances provide a standard isotopic composition for iridium in geochemical and cosmochemical studies.

The 191Ir and 193Ir isotopes are primarily used in isotope ratio measurements performed with mass spectrometry. Such analyses support geochemical tracing, provenance studies, and cosmochemical investigations where precise isotopic signatures help identify sources and processes affecting iridium-bearing materials. Because they are stable, these isotopes also serve as reference standards in isotopic calibration.

In applications beyond fundamental research, iridium's physical properties—high density, hardness, and resistance to heat and corrosion—drive its industrial uses, including high-performance alloys, electrical contacts, spark plugs, and crucibles. The stable isotopes themselves are not radioisotopes and do not provide radiometric dating information, but they are essential for accurate isotopic analyses in scientific studies.