Petoskey stones, recognized as Michigan’s state stone, are unique fossilized corals. Their intricate patterns and prehistoric origins attract enthusiasts and collectors. Their appeal lies in both their scientific significance as remnants of a Devonian-era sea and their aesthetic beauty when wet or polished. Geological forces over millions of years brought these stones from a warm, tropical sea to the Great Lakes shores.
Primary Finding Locations
Petoskey stones are found in Michigan’s Lower Peninsula, along the northern shores of Lake Michigan and Lake Huron. These areas, including the cities of Petoskey, Charlevoix, and Traverse City, are popular locations for these corals. Popular beaches include Petoskey State Park, Lake Michigan Beach in Charlevoix, Empire Beach, and East Bay Park and Old Mission Point Park in Traverse City.
Their presence results from two geological periods. About 350 million years ago, during the Devonian Period, Michigan was near the equator, submerged under a warm, shallow saltwater sea where vast coral reefs, primarily Hexagonaria percarinata, thrived. Over millennia, these corals died and were fossilized, becoming part of the bedrock.
Later, during the Pleistocene epoch, glaciers scraped and eroded the bedrock containing these fossilized corals. Glacial ice transported these fragments, depositing them across northern Michigan as it receded. This explains why Petoskey stones are found in scattered deposits on beaches, riverbanks, and even in inland gravel pits, far from their original formation sites. Lake currents and wave action continue to unearth and redistribute these stones along the shorelines.
Recognizing Petoskey Stones
Identify a Petoskey stone by its distinct visual characteristics, especially the hexagonal pattern. This pattern is the preserved skeletal structure of individual coral polyps, resembling a honeycomb. Each hexagon features a dark center (the coral polyp’s mouth) surrounded by radiating lines (the organism’s tentacles).
Stones range from light gray to dark beige, with rarer pinkish hues due to iron during fossilization. When dry, they resemble ordinary limestone. However, their unique pattern becomes visible when wet or polished, making them easier to spot along the water’s edge or when submerged.
Best Practices for Stone Hunting
Successful Petoskey stone hunting often benefits from timing and strategic searching. The best times to search are typically after strong winds or significant storms, as the churning waters unearth new stones and deposit them along the shoreline. Early spring, after the winter ice has melted and broken up, also presents an opportune period, as the ice movement can bring fresh batches of stones to the beaches. Hunting after a rain shower is also advantageous because the wetness enhances the visibility of the stone’s distinctive pattern.
When searching, focus on rocky, uncrowded stretches of beach, as sand-only areas are less likely to yield finds. Visually inspect the shallow water near the shoreline; wading into the water can often reveal stones that are not visible on dry land. Carrying a small squirt bottle or a bucket of water can be helpful to wet potential finds and confirm their patterns. If one Petoskey stone is discovered, continue searching in the immediate vicinity, as they are often found in clusters.
Adhering to collection guidelines is important to ensure the sustainability of this activity. The Michigan Department of Natural Resources permits individuals to collect up to 25 pounds of stones, minerals, or invertebrate fossils per person annually from state-owned lands. However, it is important to remember that collecting any natural items, including Petoskey stones, is strictly prohibited within National Parks, such as Sleeping Bear Dunes National Lakeshore. Always respect private property and be aware of any specific local regulations that might apply to the area you are exploring.