How to Polish Your Michigan Petoskey Stone
The beloved Petoskey stone. Nothing gets old about this 350-million-year-old fossil.
From Spring to Fall, millions of people come from all over the world to comb the shores of Northern Michigan in hopes of finding a Petoskey Stone. Memories are made during the hunt. Blue, cool, water licking ankles, toes touching sand, a breeze in your face … and then you see it … a rock looking back at you. Children and adults squeal with delight. There are high-fives all around.
But then, you get it home, intending to display your prized find and blink twice. Now it’s dry. What happened? Where did the eyes go? Is it sleeping or did it morph into a plain grey rock on the trip home? It looks nothing like the beauty you found in the water and far from the shiny, glass-like stunners you saw in the gift shops.
As an avid rockhound, I want to share my step-by-step guide to polish your treasures. It is a simple method, requiring sandpaper, time, and a lot of elbow grease. The reason Petoskey stones can be polished by hand is because they are relatively soft. On the Mohs scale of mineral hardness, from 1–10 a Petoskey scores a 3. To put it in perspective, talc scores a 1 and diamonds score a 10. This method won’t work with many other wonderful Michigan stones such as an agate, which scores an 8.
It is important to remember to always work with a wet stone. You don’t want to breathe in the dust created by sanding a dry stone. It can damage your lungs.
If you are starting with a pitted or uneven Petoskey, use a metal file to shape and smooth out the rough patches.
I do most of my polishing in the garage because it can get a bit messy. I also take off my rings, so I don’t scratch them. I set a small bucket with a few inches of water at my feet and sit on an outdoor chair with a towel on my lap to protect my clothes.
For beginners, I recommend starting with a relatively smooth stone that is “pure Petoskey,” meaning when you wet the stone, you can see the pattern clearly throughout.