Iridium
Also: Ir, Iridium Metal
Iridium (Ir) is a silvery-white platinum group precious metal with one of the highest densities of all elements (22.56 g/cm³, just behind osmium) and exceptional corrosion resistance.
Iridium belongs to the group of platinum group metals and is regarded as one of the rarest and most difficult to process metals on Earth. With a density of 22.56 g/cm³, it is the second-densest naturally occurring element – just behind the related osmium (22.59 g/cm³). It was discovered in 1803 by Smithson Tennant, who named it after the Greek goddess Iris (rainbow) because its salts appear in strikingly different colours.
Occurrence and Extraction
Iridium occurs in the Earth's crust at concentrations of around 0.001 ppb – roughly ten times rarer than gold. It is obtained almost exclusively as a by-product of nickel and copper extraction from platinum ores, mainly in South Africa (Bushveld Complex), Russia and Zimbabwe. Global annual production fluctuates between seven and nine tonnes and is thus considerably lower than that of platinum or palladium.
Properties
Iridium's technical characteristics are exceptional:
- Highest corrosion resistance of all metals: iridium dissolves neither in hydrochloric acid nor in sulphuric acid. Only aqua regia attacks it under certain conditions.
- Extremely high melting point of 2,446 °C – higher than almost all technically usable metals.
- High hardness (Mohs 6.5) combined with pronounced brittleness, which makes mechanical processing considerably harder.
Industrial Applications
Because of its resilience, iridium is used in high-temperature and high-precision applications:
| Field | Application |
|---|---|
| Automotive industry | Spark plug electrodes (Ir alloy) |
| Chemistry | Crucible material for single-crystal growth |
| Medicine | Radiotherapy (Ir-192 implants) |
| Aerospace | Rocket engines, heat shielding |
| Metrology | Historically: prototype-kilogram alloy (Pt-10%Ir) |
Iridium as an Investment and Trading Object
Unlike gold, silver, platinum or palladium, there is no established futures market (COMEX) and no daily fixing for iridium. Prices are published by industrial wholesalers such as Johnson Matthey or Heraeus as reference prices. The extreme market thinness – few tonnes of annual production, few large buyers – leads to sometimes strong price swings on small trading volumes. Iridium is primarily an industrial metal; liquid investment products (coins, ETCs) are barely available. Comparable historical price trends of the platinum group metals can be followed on the platform.
Tax and investment-advisory notes on iridium as an investment object should be checked individually – this entry does not constitute tax or investment advice.
In Brief
Iridium is the densest and most corrosion-resistant metal on Earth, arising almost exclusively as a by-product of platinum mining, and, because of its extreme rarity and the absence of liquid trading markets, it is regarded primarily as an industrial metal. Current prices of the related platinum group metals offer orientation for the price level of this market segment.