Finding Petosky Stones

While in Michigan we went to a town called Petosky. Apparently you can find special stones native only to that area called Petosky stones. WEll, we collected a ton of stones and I think only one of them is really a petosky. Can you tell which one? Me either.......

Okay so I think the one fourth from the bottom is a Petosky. See the circular patterns?

The stone second from the right on the bottom is really really clean. Matthew discovered that if you lick it the lines and patterns are more visible. He must have licked that particular stone for about twenty minutes.