They are for the quest, if you choose to help team aqua. You will be given an item that you must take into a particular stone. The stone is one of these blue stones. The other ones are lures. If you pick up the wrong stone, a wild pokemon (uncatchable I think) will appear. You must defeat the poke then and try another one.
I see,ty. I chose team magma so I was kinda clueless as to what those stones were xD