A Petoskey stone is a unique geological specimen, highly regarded in Michigan for its distinctive appearance. These fascinating objects are remnants of an ancient past, offering a tangible connection to prehistoric life. Their singular patterns and origin story make them a subject of interest for collectors and curious minds alike.
Identifying a Petoskey Stone
A Petoskey stone is most recognizable by its distinctive pattern of tightly packed, six-sided shapes, often described as a honeycomb or starburst design. Each hexagon represents the skeletal remains of an individual coral polyp, with a dark “eye” at its center and thin lines radiating outwards. These features are the fossilized structures of the coral’s mouth and tentacles.
The stone’s color ranges from light gray to beige, resembling ordinary limestone when dry. However, the characteristic hexagonal patterns become much more pronounced and visible when the stone is wet or polished. This transformation makes searching for them along shorelines, where they are naturally wet, particularly effective.
The Geological Story Behind Petoskey Stones
Petoskey stones are fossilized colonial corals, specifically Hexagonaria percarinata. These corals thrived in warm, shallow seas that covered the region now known as Michigan during the Devonian period, 350 to 400 million years ago. At that time, Michigan was situated near the equator, providing an ideal tropical environment for extensive coral reefs.
As these ancient coral colonies died, their calcium carbonate skeletons were buried by sediment and fossilized, preserving the hexagonal structure. During the Pleistocene epoch, massive glaciers moved across the landscape, plucking these fossilized corals from the bedrock, grinding them, and distributing them across Michigan’s Lower Peninsula. This glacial action, which occurred about two million years ago, is responsible for the rounded, pebble-like shape and widespread distribution of Petoskey stones today.
Significance and Where to Find Them
The Petoskey stone holds a special place in Michigan, officially designated as the state stone in 1965 through Michigan Public Act 89. This designation highlights its unique geological heritage and its connection to the state’s natural beauty. The stone’s name itself has ties to the region, honoring Ottawa Chief Pet-O-Sega, whose name means “rays of the rising sun,” a poetic description often associated with the stone’s pattern.
These stones are primarily found along the shores of Lake Michigan and Lake Huron, with concentrations around Petoskey and Charlevoix. Success often improves by looking in rocky beach areas rather than sandy ones. The best times to find them are in early spring, after winter ice movement has churned up new stones, or immediately following a storm, as the water helps reveal their distinct patterns. Many enthusiasts carry a water bottle to wet potential finds and confirm the pattern.