Micky`s Riddles award...

[Ice]

Maybe me?

At the ends of the world- Not sure.
But not in the middle- Lava is in the middle, not ice.
At heights and depths- Hail; Glacier.
Oft big, usually little- Glacier; Ice cube.
As common as dirt,- Not sure.
But deadly as venom,- Ummmm, choking?
Floating never sinking,- Ice floats.
I know that you've seen him.