Osmium is a chemical element; it has symbol Os and atomic number 76. It is a hard, brittle, bluish-white transition metal in the platinum group. It was discovered in 1803 by Smithson Tennant, who named it for the characteristic smell of its volatile oxide. Osmium has the highest density of any stable element and one of the lowest abundances in the Earth's crust, where it is mainly found alongside other platinum group metals and in ores of copper and nickel.