The Petoskey Stone is the Michigan State stone. It is a fossilized coral that lived 350 million years ago during the Devonian age. It is older than the dinosaur. The scientific name is Hexagonaria Percarinata meaning 6 sided.
It was a living flower plant animal and each hexagon was the tip of a single tentacle, which was where the food was absorbed. The coral was originally red....sometime you can still see the red in the stones.
The Petoskey stone can be found only in Michigan, usually in the northern half and mostly around Petoskey, MI. However, it also can be found far south as Cadillac. The best places to look for them is along the shores of Lake Michigan, in the lakes and streams and in the quarries.
When Polishing the Petoskey Stone using the expandable drum you will want to have water running over or under the sandpaper the whole time.Start with 220 girt paper that slides over the drum unless you tumbled it first. If you tumbled, then start with 400 grit. If the stone is very ruff, then start with 100. Using a circular motion and always moving, rub the entire stone over and over until you can feel the difference in how smooth it is. After this step, wash the stone, tray and wheel. Add the 400 grit paper and follow the same process. Then go to the 600 and 800 grits following the same process. Be sure to wash everything after each step. The last step is the polishing step.
Using muslin buffing pad, stacking 3 pad together, Use Dico polishing compounds (E3 Emery). While running, take the compound and rub the cloth with it and and rub the stone to the cloth. Then repeat with a new set of cloths and us PBC Plastic compound. If your stone is not shinny it is because you did not sand your stone enough.
If you want to If you want to polish the petoskey in a tumble, I recommend that you use a vibratory tumbler. You first fill a 4 pound barrel with stones, using a mix of sizes and then fill with some water. Then dump all the excess water out. You do not want much water in there. Then add 2 teaspoons of 220 grit and check it in an hour after running. You are looking for the stones to be covered with a grey mud. If the mud gets so think that the stones do not roll, then you will have to add a small amount of water until it rolls again. Then check in about 20 minutes. Once it thickens again it is time to rinse them off. Now you can leave them like this or finish them with the by hand method or the machine method using the expandable drum. Either method after this step, you can go to the 400 grit.
You can always polishing the Petoskey Stone by hand because they are so soft. Start with one that is already smooth. The first step will be using a 220 grit, unless you tumbled them first. If you tumbled them, go to the 400 grit. Keep the sandpaper and stone wet at all time. It will be much cleaner. You can smooth out the stone in this step. Second, you will us a 400 grit and you will feel the difference in the smoothness. Third, do the same with a 600 girt. Make sure you can feel the difference all over the stone. Then you are ready for the polishing step. Use about 1 teaspoon of tin oxide and mix with water until you have a paste and in a circular motion go over and over the stone with a piece of leather until you get a shine.
Looking for Petoskey Stones can be fun. You will be looking for the hexagon pattern with white markings separation the hexagons.The stone varies in shades of brown. Not all of them have the hexagon pattern throughout the stone. Most of them have other mineral deposits which give them character.