Osmium (from Greek ὀσμή osme, "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 22.59 g/cm3. 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.

Osmium has a blue-gray tint and is the densest stable element, approximately twice the density of lead and slightly denser than iridium.

Osmium is a hard but brittle metal that remains lustrous even at high temperatures. It has a very low compressibility. Correspondingly, its bulk modulus is extremely high, reported between 395 and 462 GPa, which rivals that of diamond (443 GPa). The hardness of osmium is moderately high at 4 GPa. Because of its hardness, brittleness, low vapor pressure (the lowest of the platinum-group metals), and very high melting point (the fourth highest of all elements), solid osmium is difficult to machine, form, or work.

More Info: en.wikipedia.org