Petoskey Stones: Your Guide to Michigan's Freshwater Fossils

At a Glance

Petoskey stones are fossilized colonial coral (Hexagonaria percarinata) from the Devonian Period, roughly 350 million years old, and are Michigan's official state stone. They're found along the northern shores of Lake Michigan, primarily around Petoskey, but also in Charlevoix, and Traverse City, with the best hunting after storms in spring and fall. Wet stones reveal their signature hexagonal pattern; dry stones look like plain gray rocks until polished. This guide from Inn at Bay Harbor covers what they are, where to find them locally, and how to finish them at home.

What Exactly Is a Petoskey Stone?

Michigan's official state stone, the Petoskey stone isn't just a rock — it's a fossil. Each one is a piece of ancient coral called Hexagonaria percarinata, a colonial coral that lived in the warm, shallow sea that covered this part of Michigan roughly 350 million years ago during the Devonian Period. Back then, Michigan was submerged under a tropical marine environment perfect for coral reefs.

Over millions of years, the remains of the coral colony fossilized. Later, glaciers scraped across the region, breaking up the ancient reef bedrock and scattering pieces across the landscape and lakebed — which is why you can find Petoskey stones scattered along beaches and in the shallow waters of Little Traverse Bay today. The name comes from the location most prevalent with them, Petoskey, Michigan.

How to Identify a Petoskey Stone

The telltale feature is the hexagonal pattern on the stone's surface — each hexagon is a single coral polyp (called a corallite), and the dot in the center is where the coral's tentacles once extended to catch food. A few identification tips:

• Wet stones show the pattern best. Dry, the stone often just looks like an unremarkable gray or tan rock, with some lines or slightly darker spots visible. Wet it with water, and its unique six-sided pattern pops into view.
• Look for texture, not just color. Petoskey stones right off the beach often have divots or ridges, and the tiny intricate lines are the first thing you spot. Run your finger over the surface — you may feel subtle ridges outlining each hexagon.
• Size varies widely. Petoskey stones range from pebble-sized fragments to boulders larger than a basketball, though most beach finds are fit in the palm of your hand. Look carefully along the Inn's shoreline boulders for 'pockets' of inlaid Petoskey stone.
• Patterns aren't always uniform. No two stones are the same, and many Petoskey stones have 'stretched' looking patterns that show off their coral origins.

Raw stones found at Inn at Bay Harbor

Where to Find Petoskey Stones Near Bay Harbor

The good news for guests staying at Inn at Bay Harbor: you're already in one of the best spots for Petoskey stone hunting. The stones are concentrated in the limestone deposits found around Little Traverse Bay, and they wash up along much of the surrounding shoreline.

A few reliable spots in the area:

• Inn at Bay Harbor's own shoreline — just steps from the hotel, our rocky shoreline and waters offer guests the chance to find stones every day
• Petoskey State Park — one of the most famous and consistently good spots, with over a mile of Lake Michigan shoreline
• Magnus Park Beach in Petoskey — easy public access near Bayfront Park with rocky shoreline
• Bayfront Park in Petoskey — a small beach on the east side of the break wall offers marina views, calm waters, and plenty of small stones
• Fisherman's Island State Park near Charlevoix — a bit further south, known for larger stones

When to Look

Timing matters as much as location for Petoskey stone hunting

• Early morning, when low-angle light makes textured stones easier to spot, and before other collectors have had a chance to pick through the best areas.
• After storms or high wind events, when wave action churns up the lakebed and deposits fresh rocks on shore.
• Spring and late fall, when water levels are lower and more shoreline is exposed.
• Shallow water hunting works well too — many serious collectors wade in with polarized sunglasses, which cut glare and make the hexagon pattern far easier to spot underwater.

Is It Legal to Collect Petoskey Stones?

Yes, for personal use. Michigan allows individuals to collect up to 25 pounds of rocks, minerals, and fossils per person, per day, from state-owned bottomlands and most public beaches, with a 100-pound annual limit. Collecting is not permitted in some protected natural areas, so it's worth checking posted signage, especially in state parks and nature preserves.

How to Polish a Petoskey Stone

A raw Petoskey stone is beautiful once wet, but a polished one keeps the pattern visible and the surface glossy — which is why so many are turned into jewelry, coasters, and keepsakes. Two common approaches:

Hand sanding (best for keeping a natural shape):

1. Start with coarse wet/dry sandpaper (around 220 grit) to knock down rough spots, sanding wet to reduce dust.
2. Progress through finer grits, up to 1500–3000, rinsing between each.
3. Finish with a polishing compound and a soft cloth, or a dab of mineral oil for an easy at-home shine.

Hand-sanding kits can be found in the Inn Cafe.

Tumbling (best for smooth, rounded stones):

1. Sort stones by size and tumble similar sizes together.
2. Run several stages of grit in a rock tumbler — coarse, medium, fine, then a polishing stage — each cycle typically running one to two weeks.
3. Rinse thoroughly between stages to avoid contaminating the next grit level.

A Little Piece of Northern Michigan to Take Home

Whether you leave with a pocketful of raw stones or a single polished favorite, a Petoskey stone is one of the most authentic souvenirs of a Northern Michigan trip — a literal piece of history from the same waters you're looking at from the hotel. Rock hunters, it's time to head out to the shoreline — you might be surprised what the lake leaves out for you.

Planning a stay at Inn at Bay Harbor? Ask our team for our current favorite nearby beaches for stone hunting — conditions change with the seasons, and we're happy to point you toward the best spots during your visit.