osmiums

Osmium is a chemical element with the symbol Os and atomic number 76. It is a hard, blue-white transition metal in the platinum group and is among the densest elements known, with a density of about 22.59 g/cm3 at room temperature. It has a very high melting point near 3045°C and is brittle, making it difficult to work with in bulk. Osmium forms a variety of oxides, the most notable being osmium tetroxide (OsO4), a volatile compound.

Osmium is extremely rare in the Earth's crust and occurs primarily in platinum-bearing ores, often in the alloy osmiridium (osmium with iridium). It is produced as a byproduct of mining and refining nickel and platinum-group metals. Its occurrence is highly localized, which contributes to its scarcity and high value in specialized applications.

The most well-known osmium compound is osmium tetroxide (OsO4), which is highly toxic and volatile. OsO4 is used in electron microscopy as a staining agent and as an oxidizing catalyst in organic synthesis in some contexts. In metallic form, osmium is used in niche wear-resistant applications and is alloyed with iridium to form osmiridium, which has historically been employed for hard, durable points and contacts, such as in fountain pen nibs and precision instruments.

Safety and handling are important for osmium compounds, particularly OsO4, due to toxicity and volatility. Proper protective equipment and fume hood containment are required, with careful disposal in accordance with regulations.

Discovered in 1803 by Smithson Tennant in England, osmium derives its name from the Greek osme, meaning odor, a reference to the distinctive smell associated with OsO4.