Osmium
Also: Os, Osmiridium
Osmium (Os, atomic number 76) is the densest naturally occurring element on Earth and belongs to the group of platinum metals.
Osmium (chemical symbol Os) was isolated in 1803 by the English chemist Smithson Tennant from the residue of platinum ores. Its name derives from the Greek osme (smell) - crude osmium compounds release the highly toxic osmium tetroxide (OsO4), which has a characteristic pungent odour. Osmium belongs to the group of platinum metals and, with a density of 22.59 g/cm3, is the heaviest naturally occurring element of all - slightly denser even than iridium.
Occurrence and extraction
Osmium is one of the rarest elements in the Earth's crust (approx. 0.001 ppb). It occurs almost exclusively as a by-product of platinum metal refining, mainly from nickel-copper ores in South Africa, Russia and Canada. Pure osmium is separated from the platinum concentrate in a multi-stage separation process - so-called affinage. Worldwide annual production amounts to only a few tonnes.
Properties
Osmium is a blue-grey lustrous, extremely hard and brittle metal. Its melting point of 3,033 C is the highest of all platinum metals. This exceptional hardness and density make it unsuitable for many manual processing methods.
| Property | Osmium | Iridium | Platinum |
|---|---|---|---|
| Density (g/cm3) | 22.59 | 22.56 | 21.45 |
| Melting point (C) | 3,033 | 2,446 | 1,768 |
| Mohs hardness | 7.0 | 6.5 | 4.3 |
Uses
The technical fields of application for osmium are limited to niche uses:
- Alloys: Combined with iridium or platinum it serves as a wear-resistant coating for fountain-pen nibs, contacts and surgical instruments.
- Catalysis: OsO4 is used in organic chemistry as an oxidising agent in fine chemistry.
- Collector market: Since about 2013, crystalline osmium - so-called "iridescent osmium" in a hexagonal crystal form - has been marketed as an investment object and gemstone. Suppliers promote it as the rarest and densest tradable element. Note: In the absence of an established secondary market and standardised price discovery (no exchange price as with the platinum price), valuation is difficult. This is not investment advice.
Price formation
Unlike platinum, palladium or rhodium, osmium is not traded on a commodities exchange and has no official spot price. Prices are negotiated bilaterally between dealers; for crystalline osmium there are specialised certification bodies. You can convert the current platinum price and other platinum-metal prices into various weight units for orientation using the unit converter.
In brief
Osmium is the densest element on Earth and an extremely rare platinum metal with highly specialised industrial applications. Crystalline osmium has attracted interest as a collector's item in recent years but has no standardised exchange market - purchase decisions require careful scrutiny.