The last time I saw a TIL about this sort of thing though it turned out that “Aluminum” was the original but some academics thought “Aluminium” sounded fancier. My understanding is that it relates to the oxide names, which in the case of aluminum is alumina, after which the -a is swapped for the -um, similar to how magnesium oxide is magnesia. But I’m too lazy to fact check.
Also Molybdenum exists too, so it’s not like Aluminum would be the one exception that is just -um and not -ium.
I guess ask the Romans about half of those.
The last time I saw a TIL about this sort of thing though it turned out that “Aluminum” was the original but some academics thought “Aluminium” sounded fancier. My understanding is that it relates to the oxide names, which in the case of aluminum is alumina, after which the -a is swapped for the -um, similar to how magnesium oxide is magnesia. But I’m too lazy to fact check.
Also Molybdenum exists too, so it’s not like Aluminum would be the one exception that is just -um and not -ium.