Name Iridium
Symbol Ir
Atomic Number 77
Atomic Mass 192.217 atomic mass units
Number of Protons 77
Number of Neutrons 115
Number of Electrons 77
Melting Point 2410.0 C
Boiling Point 4527.0 C
Density 22.5 grams per cubic centimeter
Normal Phase Solid
Family Transitions Metals
Period Number 6
Cost $500 per troy ounce (1990)



Origin of Name From the Latin word iridis, meaning rainbow
Date and Place of Discovery In 1804 in London, England
Discovered by Smithson Tennant
Common Compounds
Interesting facts
  • It is occurs in natural alloys with platinum or osmium.
  • It is the most resistive to corrosion - it cannot be attacked by acids or aqua regia - but can be attacked by molten salts such as NaCl or NaCN.
  • It is very brittle making it difficult to work with.
  • It is only a little less dense than osmium, the most dense element.
Common Uses
  • High strength alloys that can withstand high temperatures
  • Electrical contacts
  • Hardening agent for platinum
  • Crucibles
  • Compass bearings
  • LED technology
  • Radiation therapy to treat prostate and other cancers
  • Spark plus for internal combustion engines
  • Fountain pen nibs


Photo Courtesy of
Chemical Elements
All Metals & Forge
Jefferson Labs
Los Alamos National Labs

Iridium Atomic Structure Elements by Name Elements by Number