The densest of the elements, osmium, is a blue-gray hard member of the platinum group metals (PGM). Osmium is a trace element in platinum ore and was discovered in 1803 by British chemist Smithson Tenant from samples provided by William Hyde Wollaston, discoverer of platinum. Tenant named the metal for the Greek "smell" because of the odor associated with it oxidizing in air.
Since discovery, osmium has not had a very glamorous treatment for a noble metal. Though quite rare, it is not considered attractive and so is not priced as a precious metal. In addition, as it oxidizes in air, it creates volatile OsO4. Osmium tetroxide is toxic, which discourages use of the pure metal.
Mining and Production
Osmium is found naturally alloyed with iridium and as a trace component with other PGMS in deposits of nickel and copper ores. It is therefore mainly produced as a byproduct of platinum extraction, primarily in South Africa, Russia, and Canada.
Refining of nickel or copper by electrolysis leaves a residue that contains several PGMs. The noble metals are not that similar to each other chemically; they react differently to a series of well-chosen solvents and can be separated. Osmium is usually produced as a powder because its hardness makes it difficult to shape. The actual amount produced each year is tiny (less than a ton).
Properties and Uses
Almost all uses of osmium involve alloying it with iridium or other PGMs for hardness and corrosion-resistance. For example, osmium alloys are the traditional choice for pen nibs, electrical contacts, compass needles, and other high-wear situations. Osmium-tungsten was used in early light bulb filaments. Osmium-platinum is used to make surgical instruments because of its inertness.
Osmium tetroxide, being volatile and strongly oxidizing, is useful in the chemical industry, as long as precautions are taken. The simplest application is staining biological samples for inspection under a microscope.
Although osmium is the densest metal, just beating out iridium, that seems not to be important commercially.
Osmium is not a practical investment choice. Among the PGMs, platinum and palladium have healthy financial markets. Iridium and rhodium spot prices are published by Johnson Matthey. Prices for the remaining two metals, osmium and ruthenium, are theoretically available from a couple of sources. But, as the flat line in the graph shows, these spot prices are just a starting point for negotiations.
The tiny amount of osmium used by industry each year for specialized purposes does not leave room for investors to participate, nor is bullion osmium (because of toxicity) a reasonable option.