Petoskey stones are a fossilized coral found mainly in northern MI. Hexagonaria percarinatae is the scientific name for the coral. They date back to the Devonian period and are 355-415 million years old. They became Michigan's state stone in 1965. Petoskey stones will have a whitish-gray when dry and a gray when wet.They have "eyes" about the size of a pencil. The eyes are grouped like a bunch of pencils. Most stones with take a good polish.
The best place to look for stones is in the Petoskey area and around Alpena. Look for them on the beach, around gravel pits and road cuts. When looking for Petoskey stones it is handy to have a spray bottle full of water to spray the stones down to see the eyes. After a rain when the rocks are still wet is another good time to find stones.