Symbol Os. A hard blue-white metallic transition element; a.n. 76; r.a.m. 190.2; r.d. 22.57; m.p. 3045°C; b.p. 5027°C. It is found associated with platinum and is used in certain alloys with platinum and iridium (see osmiridium). Osmium forms a number of complexes in a range of oxidation states. It was discovered by Smithson Tennant (1761–1815) in 1804.
http://www.webelements.com/webelements/elements/text/Os/key.htm Information from the WebElements site