Porch Notes
That Pretty Beach Rock Is a 350-Million-Year-Old Coral
Outdoors
Michigan’s official state stone is not just a pretty beach rock. It is a piece of fossil coral older than the dinosaurs.
Meet the Petoskey stone. When it’s dry, it looks like a plain gray pebble. But get it wet (or polish it) and a gorgeous honeycomb pattern appears, like a cluster of tiny six-sided sunbursts. Those “sunbursts” are the fossilized skeletons of a colonial coral called Hexagonaria percarinata, which lived about 350 million years ago during the Devonian Period — back when what we now call Michigan sat near the equator under a warm, shallow tropical sea. Glaciers later broke up the ancient reef, smoothed the pieces, and scattered them across northern Michigan.
The stone got its name from Chief Petosegay, a respected Odawa fur trader whose name meant something like “rays of dawn” — a fitting match for those sunburst fossils. The city of Petoskey is named for him too. In 1965, Michigan made the Petoskey stone its official state stone.
One word of friendly warning: the Department of Natural Resources limits how much you can take from state land — no more than 25 pounds of rock per year. (Yes, this is a real rule. In 2015 the DNR confiscated a 93-pound Petoskey stone someone hauled out of the lake.)
Where to see it
The Lake Michigan beaches from Traverse City up to Petoskey are the classic hunting grounds — Petoskey State Park on Little Traverse Bay is a favorite. Spring, after the lake ice churns up the shoreline, is the best time to look.