Petoskey stones are beautiful stones that can be found littered along the sandy beaches of northern Michigan. Petoskey stones, in fact, are the state stone of Michigan. These stones are actually fossils of colonial corals that lived in the seas that once covered northern Michigan in the Devonian time about 350 million years ago. When Petoskey stones are polished, the small hexagonal individual corals can be seen. If you are inclined to polish a Petoskey stone, you will find that it takes a bit of time, but is relatively easy.
Rub the stone back and forth over the 220 grit sandpaper. You can place the sandpaper on the ground and rub the stone back and forth, or place the stone on the ground and rub the sandpaper across it. Which you do depends on your comfort level and the size of the rock. Continue sanding the stone with this grit sandpaper until surfaces' blemishes are gone and the stone has a smooth surface. It may be useful to wet the stone and the sandpaper.
Sand the stone with the 400 grit sandpaper. Do this in the same manner as when you used the 220 grit sandpaper. The stone should become even smoother. Continue to use this grit sandpaper until the entire stone is smoother than it was previously, and all the coarse spots are gone.
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Sand the stone with the 600 grit sandpaper. Do this in the same manner as when you used the rougher sandpaper. Continue to use this grit sandpaper until the entire stone is smoother than it was previously and all scratches are gone. Then sand with this grit sandpaper for another 10 to 15 minutes.
Wet the velvet or leather strip with water, and sprinkle it with polishing powder. Using short rotating strokes, rub this paste all over the surface of the stone. This will bring a shine to the rock.
Rinse the rock and dry it off. If there are any scratches or dull spots that remain begin the process again with the 220 grit sandpaper.
This will take a lot of time!