Osmium
OSMIUM Osmium was discovered in 1804 by Englishman Smithson Tennent in the residue left by dissolving platinum in aqua regia. Osmium is generally credited as the heaviest and most dense element. ... The symbol for osmium is Os. ... The crystal structure of osmium is hexagonal. Osmium metal is lustrous, bluish white, extremely hard, and brittle even at high temperatures. ... The solid metal is not affected by air at room temperature, but the powdered or spongy metal slowly gives off osmium tetroxide, which is a powerful oxidizing agent and has a strong smell.