Osmium (from Greek osme (ὀσμή) meaning "smell") 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 . Its alloys with platinum, iridium, and other platinum group metals are employed in fountain pen nibs, electrical contacts, and other applications where extreme durability and hardness are needed.