Iridium (Ir)


  • Symbol: Ir
  • Atomic Number: 77
  • Atomic Weight: 192.217
  • Element Classification: Transition Metal
  • Discovered By: Smithson Tennant
  • Discovery Date: 1803
  • Name Origin: From the Latin ‘iris’, meaning rainbow, referring to the various colors of its salts
  • Density(g/cc): 22.56
  • Melting Point: 2446°C
  • Boiling Point: 4428°C
  • Appearance: Silvery-white, very hard, brittle metal
  • Atomic Radius(pm): 136


Iridium was discovered in 1803 by English chemist Smithson Tennant. Tennant isolated iridium while examining the residues left after dissolving platinum ore in aqua regia. Alongside osmium, iridium was identified as a new element through its colorful salts. The name “iridium” originates from the Latin word ‘iris’, meaning rainbow, highlighting the varied hues of its compounds. This discovery underscored the complexity and diversity within platinum group metals.

Relation to Other Elements

Iridium is a member of the platinum group metals (PGMs), which includes platinum, palladium, rhodium, ruthenium, and osmium. These metals are characterized by their excellent resistance to corrosion, high melting points, and significant catalytic properties. Iridium, in particular, is noted for having one of the highest densities and melting points among all metals, making it extremely durable and wear-resistant. Its scarcity in the Earth’s crust further emphasizes its value and uniqueness.

Natural Occurrence

Iridium is one of the rarest elements in the Earth’s crust. It occurs naturally in alloys with other platinum group metals in alluvial deposits and within nickel and copper mining ores. The largest producers of iridium include South Africa, Russia, and Canada. Due to its rarity, iridium is primarily obtained as a byproduct of nickel and platinum refining.


Iridium’s unique properties lead to several specialized applications:

  • Electronics and Electrical: Iridium is used in spark plugs, electrodes, and electrical contacts for its high melting point and corrosion resistance.
  • Catalysis: Like other PGMs, iridium serves as an effective catalyst in chemical reactions, including the Cativa process for acetic acid production and electrolysis for water splitting.
  • Crucibles and Equipment: High-purity iridium is used to make crucibles and other equipment for high-temperature scientific research, given its exceptional thermal stability.
  • Medicine: Iridium-192, a radioactive isotope, is used in brachytherapy for the treatment of certain cancers, exploiting its targeted radiation delivery.

The discovery of iridium contributed significantly to the advancement of materials science, particularly in areas requiring materials that can withstand extreme conditions. Its applications in catalysis, electronics, and medicine highlight the critical role of even the rarest elements in driving technological progress and improving quality of life.

Osmium (Os)

Platinum (Pt)