Iridium

Iridium is an extremely hard and brittle metal, making it difficult to machine and form. The high costs involved in forming cause the cost per gram to rise sharply when formed from the basic material into a wire or foil. Iridium is the most corrosion resistant metal known, and can act as a hardening agent when alloyed to elements such as gold and platinum.

It is also used for making crucibles and other high temperature apparatus. Other applications include use in Pt/Ir spark plugs and electrical contacts.