The Petoskey Stone, recognized as Michigan’s state stone, is a sought-after fossil that captures a deep history in its unique appearance. This prized discovery for beachcombers and rockhounds is a tangible remnant of a time when the region was covered by a warm, shallow sea. The stone’s fascination comes from its transformation from a dull, gray pebble into a striking piece of natural art when polished or wet.
Defining the Petoskey Stone
The Petoskey stone is the fossilized remnant of a colonial rugose coral, specifically identified as Hexagonaria percarinata. This ancient organism thrived approximately 350 million years ago during the Devonian Period, when the landmass that is now Michigan lay near the equator. The stones are composed of calcite, which formed as the original coral skeletons were replaced through the process of fossilization.
When dry, a Petoskey stone typically resembles ordinary gray or tan limestone, often blending in with other beach rocks. However, wetting the surface instantly reveals the fossil’s distinctive pattern. This pattern consists of tightly packed, six-sided shapes known as corallites, each with thin lines radiating out from a dark center, which was the mouth of the ancient coral polyp.
The Primary Search Region
Glacial movements during the Pleistocene Epoch scraped up large sections of the coral-rich bedrock, known as the Traverse Group, and scattered the fragments across the northern Lower Peninsula. As a result, the highest concentrations of these fossils are found in the northwestern portion of Michigan’s Lower Peninsula, particularly around the city of Petoskey and Little Traverse Bay.
The continuous action of the Great Lakes, especially Lake Michigan and Lake Huron, is responsible for polishing these fragments and depositing them along the shorelines. Wave action and shifting ice sheets constantly grind and tumble the stones, exposing fresh specimens on the beaches each season. This process makes the rocky lake shores the most productive search areas.
Specific Public Collecting Sites
The most reliable places to search for Petoskey stones are the public beaches and state lands bordering Lake Michigan in the northern part of the Lower Peninsula. Petoskey State Park, located on Little Traverse Bay, is a well-known and accessible location for rock hunting, offering miles of shoreline where the stones can be found. Beaches around the city of Charlevoix, including Fisherman’s Island State Park and North Point Nature Preserve, are also highly recommended due to their proximity to the geological source of the fossils.
Searching is often most fruitful in areas with a mix of sand and gravel, rather than purely sandy beaches, as the stones are heavier and tend to collect in rocky areas. The best time to look is in the spring, after winter ice has churned the lake bottom and deposited new rocks. Searching immediately following a strong storm that washes fresh material onto the shore is also productive.
Rules for Ethical Collection
Collecting Petoskey stones on public land is generally permitted, but specific rules and quantity limits must be observed. The Michigan Department of Natural Resources (DNR) allows individuals to collect up to 25 pounds of stones, minerals, or fossils per year from state-owned bottomlands and state parks.
Collecting is strictly prohibited on federal lands, such as within the boundaries of Sleeping Bear Dunes National Lakeshore, where all natural objects must be left in place. Additionally, collectors must always respect private property boundaries and obtain explicit permission before searching on any non-public land. The use of mechanical equipment or extensive digging to extract stones is forbidden on state lands, meaning collection should be limited to surface-level finds.