August, SKI Tips, 2026

Michigan’s most prized natural treasure
By Ann Wolski
On a recent trip to Michigan, I learned about the state’s most prized natural treasures—Petoskey stones. Named after the town of Petoskey on the shores of Lake Michigan, these fascinating stones are only found in Michigan where they originated from a type of coral reef system that thrived in Lake Michigan during prehistoric times.

Petosky stones are fossilized skeletons of colonial rugose corals--Hexgonaria percarinata—that lived roughly 350 million years ago during the Devonian period when Michigan sat near the equator under a warm shallow sea. About two million years ago, glaciers plucked those fossils out of the bedrock, ground off the edges, and scattered them primarily across northern Michigan.  That’s why you find them loose on beaches instead of locked in stone.

Petosky stones aren’t rare, but they’re not easy to spot. Their hexagon patterns are hard to see when dry, but when wet or polished, they almost look manmade. Nature, however, has been crafting them for hundreds of millions of years. Each Petoskey stone is packed with six-sided cells called corallites, and the dark dot at the center of every hexagon was a single coral polyp’s mouth.

Here are seven tips that will help you in your Petoskey search:

1. Early spring—April to June—is the best time to search for Petoskey stones, before the summer beach crowds descend.
2. Carry a spray bottle or work the waterline where the waves keep everything wet. A quick spray will confirm whether you have a Petosky stone or not.
3. Hunt after a storm. Waves churn stones up from the lake bottom and lay down a fresh layer.
4. Petrosky stones hide in mixed gravel not sandy beaches.
5. Look above the waterline too. Around unrooted trees, in disrupted soil, along the base of bluffs.
6. When you find one, stop walking. Petoskey stones cluster, because the glaciers that dropped them dropped them in patches.
7. Bring a small bucket, not just a spray bottle. Scoop lake water and pour it over a whole patch of gravel at once so you clear a section instead of one stone at a time.

Collecting Petosky Stone State rules:

1. You may collect up to 25 pounds per person per year on state-owned land. Collected stones over 25 pounds may be confiscated by the DNR.
2. No collecting from National Lakeshores, National Forests or National Recreation Lands.
3. If it’s private property, you must get permission from the landowner.  

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