Osmium

Osmium is the rarest of the noble metals with a worldwide annual production usually in the range of a few thousand ounces.84 It is alloyed in conjunction with ruthenium to other noble metals for use in electrical contacts, non-rusting pivots for small instruments, and fountain pen tips. Osmium’s corrosion resistance is lower than most other noble metal, being attacked by halogens, some salt solutions, and hot acids. Osmium powder will slowly oxidize at room temperature to form osmium tetroxide.