I-rid'i-ŭm, n.

n. [N. Lat., from Lat. iris, iridis, the rainbow.] (Chem.) One of the metallic elements, having a density of from 19.3 to 21.12, and thus being the heaviest of known substances.

Iridium is found native as an alloy with osmium in lead-gray scales, rarely also with platinum. It is very hard and unmalleable, has not yet been fused, and resists the action of acids except when alloyed. Its chemical equivalent is 99. Iridium takes its name from the iridescence of some of its solutions. Dana.