Ir

Iridium (Ir) is a chemical element with atomic number 77. It is a hard, dense, silvery-white transition metal and belongs to the platinum group. Iridium is notable for its extreme density, high melting point, and exceptional resistance to corrosion and oxidation.

Iridium has a density of about 22.56 g/cm3 and a melting point around 2,446°C, making it one of the most heat-tolerant and durable metals known. It resists attack by most acids and is highly stable at high temperatures, properties that underpin many of its industrial uses. It is a member of the platinum group metals, and is typically found in nature in ores containing platinum and other PGMs.

The element was discovered in 1803 by Smithson Tennant in London, who analyzed dissolved platinum ore and identified iridium and osmium as new elements. The name iridium derives from the Greek goddess Iris, reflecting the colorful salts that iridium compounds can form.

Iridium is very rare in Earth's crust. It is usually obtained as a byproduct of refining nickel or platinum ores and is frequently recovered from placer deposits containing PGMs. Its unique combination of density, stability, and high-temperature performance makes it valuable for specialized applications.

Common uses include crucibles and equipment for high-temperature chemical reactions, electrical contacts, and hard-wearing components such as pen nib tips. Iridium compounds and alloys are employed as catalysts and in certain electrochemical and industrial processes. Radioisotopes of iridium, notably iridium-192, have applications in industrial radiography and cancer treatment. Natural iridium exists predominantly as two stable isotopes, Ir-191 and Ir-193, with several radioactive isotopes having varying half-lives.