Iridium [Ir, 77]

Iridium was, presumably, emitted in higher amounts with volcanic dusts, and later on, was deposited in sedimentary rocks. Increased Iridium contents in sedimentary rocks, at the border layer between Cretaceous and Paleogene deposits, is apparently related to an effect of the meteorite collision, 65 million years ago. Various Iridium salts and organometallic compounds are used in industrial catalysis. Additionally, Iridium is used as a source of gamma radiation for the treatment of cancer, especially when a sealed radioactive source is placed inside or next to the area requiring treatment. Main oxidation state of iridium is +4, but it may vary from +2 to +6, and has 34 radioisotopes. It occurs as natural alloys with Rh and Os, mainly in arsenosulfide minerals. Its typical minerals are irarsite and hollingworthite. It may also be associated with other minerals, including olivine and ilmenite.