Osmium
Also: Os, Osmiridium
Osmium (Os, atomic number 76) is the densest naturally occurring element on Earth and belongs to the platinum group of metals.
Osmium (chemical symbol Os) was isolated in 1803 by the English chemist Smithson Tennant from the residue of platinum ores. Its name comes from the Greek osme (smell) — crude osmium compounds release the highly toxic osmium tetroxide (OsO4), which gives off a sharp, distinctive odour. Osmium is a member of the platinum group metals and, at a density of 22.59 g/cm3, is the heaviest naturally occurring element of all — a shade denser even than iridium.
Occurrence and extraction
Osmium is among the rarest elements in the Earth's crust (roughly 0.001 ppb). It appears almost exclusively as a by-product of platinum group metal refining, chiefly from nickel-copper ores in South Africa, Russia and Canada. Pure osmium is separated out of the platinum concentrate through a multi-stage refining process — so-called affinage. Worldwide annual output amounts to only a few tonnes.
Properties
Osmium is a bluish-grey, lustrous, extremely hard and brittle metal. Its melting point of 3,033 C is the highest of all platinum group metals. This exceptional hardness and density make it unsuitable for many manual fabrication processes.
| 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 applications of osmium are confined to niche roles:
- Alloys: combined with iridium or platinum it serves as a wear-resistant coating for pen nib tips, contacts and surgical instruments.
- Catalysis: OsO4 is used in organic chemistry as an oxidising agent in fine-chemical synthesis.
- Collector market: since roughly 2013 crystalline osmium — the so-called "iridescent osmium" in hexagonal crystal form — has been marketed as an investment object and gemstone. Sellers promote it as the rarest and densest tradeable element. Note: with no established secondary market and no standardised pricing (there is no exchange price as there is for 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 use the current platinum price and other platinum-group prices as a reference and convert them into various weight units with the unit converter.
In brief
Osmium is the densest element on Earth and an extremely rare platinum group metal with highly specialised industrial uses. Crystalline osmium has drawn interest as a collector item in recent years, but it lacks a standardised exchange market — any purchase demands careful scrutiny.