Iridium Ore is the compressed form of iridium, a rare metal from Industrial Craft 2 that never generates underground as a mineable vein. According to the official IC2 wiki, iridium is found through exploration: most often as Iridium Shards in the Overworld (never in the Nether), and sometimes in End Cities. A powered Compressor presses those shards into Iridium Ore, while the Macerator grinds the ore back into shards with no material loss, so the two forms convert in both directions. Iridium Ore has been part of the mod since Minecraft 1.6.4, and the data on this page is taken from the Industrial Craft 2 Experimental jar for Minecraft Java Edition 1.12.2 on Minecraft Forge.

Iridium Ore serves one purpose: the ore is the component for the Iridium Plate, a top-tier part of late Industrial Craft 2 technology. Because hunting shards across the world takes days, the official wiki recommends scanning the first Iridium Ore in the Scanner — about 850,000 EU (Industrial Craft 2's energy unit) per scan at 512 EU per tick — and replicating afterwards: the Replicator accepts up to 2048 EU per tick and rebuilds one Iridium Ore from 120 mB of UU-Matter, the universal liquid produced by the Mass Fabricator. Replication turns iridium from a finite exploration prize into a renewable resource. Scan the first ore that leaves the Compressor, and every later copy prints right at the base.