Is it one of those things like how Amrit pronounces London?
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The issue all stemmed from the guy who first named it. It had other names first, but then he (a Brit of some flavor, as I recall) called it Aluminum. That's how it became known in the US as well. Then the UK science committee or whoever said they didn't like that, it wasn't in line with the other element naming patterns, and changed it to Aluminium.
Yanks, as we often do, ignored it, because we hate extraneous letters in a lot of words for no good reason.