Osmium is a material which belongs to the platinum group of elements and is represented by the atomic symbol, Os. Its atomic number is 76, and its atomic weight is 190.2. It is a bluish-white metal that has a melting point of about 5491.4°F (3033°C). Like platinum, osmium acts as a catalyst to promote chemical reactions. Because osmium is extremely hard, the metal and its alloys are very resistant to wear and tear.

For several decades during the 1700s, scientists knew how to extract the valuable metal platinum by dissolving its ore in a mixture of nitric acid and hydrochloric acid. But a stubborn residue of black powder was always left behind, and pure platinum was hard to obtain. Although many chemists suspected that the black powder could contain other metals, the first person to isolate and characterize them was Smithson Tennant, a British chemist. After identifying one new metal as iridium, Tennant discovered a second element in 1804. He named this new metal osmium, from the Greek word for odor (osme), because compounds containing this precious metal have a distinctive smell.

Osmium is produced from the same ores that contain platinum. Certain rare earth metals related to the platinum group were of great interest to Austrian chemist Karl Auer (1858-1929), who was also known as the Baron von Welsbach. In the late 1800s, delicate carbon filaments were used in the newly invented incandescent electric light bulb. To improve electric lighting, Auer invented a longer-lasting filament made of osmium in 1898. Although this metal was too expensive for commercial bulbs, Auer had paved the way for development of other metallic filaments. Within a decade, American chemist Irving Langmuir (1881-1957) had invented the tungsten filament, which is still used in today's bulbs.

Fountain pen tips, phonograph needles, and electrical devices are often made of osmium alloys. However, osmium and its alloys are too hard to work into the shapes needed for these products, so the metals must be either cast in a mold or fabricated from their powdered form.

Besides being hard, osmium is also very dense—about twice as heavy as lead. Osmium's most important compound is osmium tetroxide (OsO₄), which acts as a powerful oxidizing agent; however, the compound is very poisonous. Pure osmium, which is also extremely hazardous, can cause blindness.

Osmium has been used to produce high-molecular weight polymers with carbohydrates. These polymers have shown some promise as treatments for arthritis.