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countable and uncountable, plural iridiums
(uncountable) A chemical element (symbol Ir) with an atomic number of 77: a very hard, brittle, silvery-white transition metal of the platinum group. quotations examples
Iridium is extremely rare on the surface of the earth but much more common in meteorites.
2014, Elizabeth Kolbert, The Sixth Extinction: An Unnatural History, Picador, page 75
(countable) A single atom of this element. examples