Much of the upper portion of southern Michigan’s bedrock originates from the Devonian and is rich with fossil material. The Traverse Group rock layers, where Petoskey stones are found, are present primarily in the northernmost part of the Lower Peninsula in a band that stretches from Lake Michigan to Lake Huron. Though the entire group contains Petoskey stone and specimens can be found throughout the uppermost portion of the Lower Peninsula, the rocks are most exposed in the Little Traverse Bay area, particularly near Petoskey and Charlevoix. In those areas, Petoskey stones are more highly concentrated, making local beaches, dunes, and gravel-rich areas prime hunting locations.
The specimen above is from Michigan, while the specimen to the right is from Morocco; while both are of the Hexagonaria group and of Devonian age—and are visually similar—only the Michigan example can be called Petoskey stone because of where it originated.