Iridium
Also: Ir, Iridium metal
Iridium (Ir) is a silver-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 in concentrations of about 0.001 ppb - around ten times rarer than gold. It is obtained almost exclusively as a by-product of nickel and copper extraction from platinum ores, predominantly 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
The technical characteristics of iridium are exceptional:
- Highest corrosion resistance of all metals: iridium dissolves in neither hydrochloric nor sulphuric acid. Only aqua regia attacks it under certain conditions.
- Extremely high melting point of 2,446 degrees C - higher than almost all technically usable metals.
- High hardness (Mohs 6.5) combined with pronounced brittleness, which considerably complicates mechanical processing.
Industrial applications
Because of its durability, iridium is used in high-temperature and high-precision applications:
| Area | 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, no established futures market (COMEX) and no daily fixing exists for iridium. Prices are published as reference prices by industrial wholesalers such as Johnson Matthey or Heraeus. The extreme market tightness - a few tonnes of annual production, few large buyers - leads to sometimes sharp price swings on small trading volumes. Iridium is primarily an industrial metal; liquid investment products (coins, ETCs) are barely available. Comparable historical price developments of the platinum group metals can be tracked on the platform.
Tax and investment-advisory notes on iridium as an investment object should be assessed individually - this entry does not constitute tax or investment advice.
Key takeaway
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 primarily regarded as an industrial metal. Current prices of the related platinum group metals offer orientation for the price level of this market segment.