Yes, the metal you get for Sir Sarles. Get the illithium and the illithium alloy, but make sure you upgrade the mace before talking to Sir Sarles (or hide the illithium in a chest) because otherwise you give him the real illithium and get stuck with the alloy. Not knowing this until after saving, I'm STILL stuck with the damn alloy. Can't upgrade the mace with alloy!
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"I'm sorry, did I kill you?"