Actually that's our fault.
Aluminum is actually the original - it was us what put in the extra 'i' - I think to make it sound more 'French'.
(
Je suis un vagabond is an unfunny, up your own arse middle class knob,
Thu 9 Jun 2011, 11:19,
archived)
To keep it in line with plutonium, rubidium, gallium etc.
Whether or not the "ium" ending is French; bof. {shrugs Gallicly}
(
SteamedCleaner,
Thu 9 Jun 2011, 11:42,
archived)