I wasn't really talking about the Avatar universe, although I used that example. But yeah, in the classical sense lightning would be fire, but I was talking more the way it would work more "realistically," if such a word can be used for such a ridiculous concept!
Of course if you could animate rock and Earth that one would have some appeal too. Imagine an army of rock golems at your command? (Not "rock golems" as in golems who like rock music, but rather golems made of rock.) That would be pretty badass.