191Ir

191Ir is a stable isotope of the element iridium (chemical symbol Ir) with a mass number of 191. It is one of the two naturally occurring iridium isotopes, the other being 193Ir. In natural iridium, 191Ir makes up about 37% of the atoms, while 193Ir accounts for around 63%.

As a stable isotope, 191Ir does not undergo radioactive decay under normal conditions and has no known radioactive half-life. Its stability means it contributes to the natural isotopic composition of iridium found in the Earth's crust and in geological samples without posing radiological hazards.

Natural iridium is a rare, dense transition metal and a member of the platinum-group elements. Commercial iridium is typically obtained as a by-product of nickel and copper mining and refining. It is used in specialized applications such as high-temperature alloys, electrical contacts, crucibles, and inert environments for industrial processes. The stable isotopes of iridium, including 191Ir, are also relevant in isotopic analysis and geochemical studies, where precise measurements of natural isotope ratios aid in understanding metal sources and processes.

Overall, 191Ir is one of the principal, non-radioactive constituents of natural iridium, contributing significantly to its isotopic composition and to applications that rely on stable isotope measurements.