The levistone you won't find until later. You need to beat the boss of the cave you're in before you can advance to where the levistone is. It's found after you beat the second of the four fiends in Gulg Volcano, which is more-or-less where you go after the Terra Cavern.

You could go where the levistone is now, but you won't be able to retrieve it until you've beaten the first of the fiends.