Petoskey stone is a fossilized coral, the state stone of Michigan and is commonly found along the shores of Lake Michigan and Lake Huron in the United States. It was formed by the fossilization of ancient coral, hexagonaria, that lived in warm shallow seas that covered Michigan during Devonian time, some 350 million years ago. As you can see in the pictures below, this Petoskey Stone has been beautifully polished on all sides. The specimen is 4-1/2" long by 3-1/2" wide and weights about 1-1/2 pounds.