This was found diving in about 15 feet of water about 100 yards on the west coast of Cape Breton. I hope the picture show the rows of dimples and preciseness of the rows. It appears to be stone and is slightly curved.
Well does it look like its broken off or in half? If it is stone it might actually be part of a rare pottery stamp. I would say Check Stamp type of paddle but you say its stone and they did have stone stamps for pottery.