Where did the 5 Mana types in Magic: The Gathering come from?

I was curious if anyone knows where Richard Garfield drew inspiration for the five-color/type magic system used in Magic: The Gathering. It is clearly not based on the Chinese elemental wheel or any other real world system I can find. I seem to recall an old interview where he mentioned the idea of "Mana" is Polynesian, but I think that was referring to just the NAME.