Iridium (Ir) is a very hard and brittle, exceptionally corrosion-resistant, silvery-white metallic element. Iridium is a transition element and a member of the platinum group. It occurs in platinum ore and is used principally to harden platinum and in high-temperature materials, surgical and scientific instruments, electrical contacts, pen tips, and and wear-resistant bearings. It is also used to encapsulate radioactive fuels on spacecraft. Discovered by Smithson Tennant in London in 1803, its name comes from the Latin iris (stem irid-) for "rainbow," from the variety of colors in gives in solution. Its most common isotope is ¹⁹³Ir (62.6%).