Osmium is commonly described as the densest naturally occurring element.
Osmium has atomic number 76 and the symbol Os. Its measured density is about 22.59 grams per cubic centimeter at room temperature, narrowly exceeding the density of iridium in commonly cited measurements. Because density values can vary slightly with temperature, crystal structure, and measurement method, scientific references sometimes discuss osmium and iridium as extremely close competitors.
Osmium is a hard, brittle, blue-gray transition metal in the platinum-group metals. It occurs naturally in platinum ores and in alloys with other platinum-group elements. The pure metal is rarely used in bulk because powdered or finely divided osmium can form osmium tetroxide, a volatile and highly toxic compound.
Osmium compounds and alloys have specialized applications, including wear-resistant tips, electrical contacts, and scientific instruments. Its name comes from the Greek word osme, meaning smell, referring to the intense odor of osmium tetroxide.