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|Iridium is a brittle and extremely hard metal. It is extremely inert chemically, resisting even the action of aqua regia. Iridium is used chiefly as an alloying material for platinum; the alloy, containing about 10 percent iridium, is much harder than pure platinum. Platinum-iridium alloys containing larger percentages of iridium are used in making precision instruments, needle points, surgical lasers and tools.