Osmium is a chemical element with symbol Os and atomic number 76. It is a hard, brittle, bluish-white transition metal in the platinum group that is found as a trace element in alloys, mostly in platinum ores. Osmium is the densest naturally occurring element, with a density of 22.59 g/cm 3. Its alloys with platinum, iridium, and other platinum-group metals are employed in fountain pen nib tipping, electrical contacts, and other applications where extreme durability and hardness are needed.
76 is the atomic number and the atomic mass for osmium is 190.23 amu
Osmium is lustrous, silvery metal, one of the so-called platinum group of metals. It is the densest metal known, although only by the narrowest margins. Osmium is unaffected by water and acids, but dissolves with molten alkali. Osmium powder reacts slowly with the oxygen of the air and gives off detectable amounts of osmium peroxide vapor.
Osmium is mainly found alloyed with other platinum metals, from which it is recovered commercially. The most important ores are either iridosmine and osmiridium.
Less of 100 kg are produced each year. There is little demand for the metal, which is difficult to fabricate.