iridium rings are jewelry that is fashioned out of the precious metal iridium. Iridium is an extremely hard, brittle and silvery white metal which is the second densest material in the world (after osmium). Pure iridium is very brittle and it could probably not be made into a jewelry item like a ring but it is used in platinum-iridium alloys such as PT950 (95% platinum with 5% iridium) and palladium-iridium alloys such as PD950 (99% platinum and 5% iridium).
These alloys are what most jewelers use when they make iridium rings. Iridium itself is very expensive, but it also has a superior luster and durability to platinum and tungsten. Iridium is used in high performance spark plugs, crucibles for recrystallization of semiconductors at high temperatures and electrodes for the chloralkali process.
Iridium has many unique properties that make it highly desirable for a variety of applications, including its extreme hardness, high melting point and resistance to corrosion. These same qualities also make iridium one of the most difficult metals to work with.
Iridium has only recently become available in a form that is suitable for making rings and other jewellery items. It is still quite rare to find 100% iridium rings as most jewelers have not invested in the equipment needed to work with this remarkable metal.