Osmium

Osmium packs about 22.6 grams into every cubic centimetre, which is roughly twice as dense as lead and more than 22 times denser than water.

Iridium is almost as dense (about 22.56 g/cm³), and the two are so close that the order depends on the calculation method. Guinness and standard references give osmium the title.

Context

Osmium has atomic number 76 and was discovered in 1803 by English chemist Smithson Tennant, who found it in the residue left after dissolving platinum ore. Its name comes from a Greek word for smell, because one of its oxides has a sharp odor.

Its density is not measured by weighing a perfect block. It is calculated from the spacing of atoms in its crystal structure, found by X-ray diffraction, together with atomic mass. Because iridium's value is so close, the ranking has been debated over the years, and small differences in the data used can change the order.

Osmium is rare and hard to work, and its alloys are used in applications such as pen tips and electrical contacts. Its oxide is toxic. The density figure depends on temperature, and 22.59 is the value commonly quoted near room temperature. For everyday comparison, a cube of osmium about the size of a sugar cube would weigh roughly as much as a small bar of chocolate, given its density of about 22.6 grams per cubic centimetre.