Osmium

Osmium is a hard, brittle, blue-gray platinum-group transition metal and the densest stable element. It is rare in Earth's crust and occurs mainly alongside other platinum-group metals and in copper- and nickel-bearing ores. Osmium alloys are used where exceptional hardness and durability are needed, including in electrical contacts and fountain-pen nibs. Osmium compounds also have important laboratory uses, including electron microscopy and the production of vicinal diols; osmium tetroxide is toxic.