Iridium is named from the Latin iris, rainbow and was discovered in 1803. Iridium is a member of the platinum group of metals, is white, very hard and brittle. It is recovered as a by-product of the nickel mining industry and is the most corrosion resistant metal known. Its principal use is as a hardening agent for platinum. With osmium it forms an alloy which is used for tipping pens and compass bearings. Iridium is one of the densest known elements.