What is a Petoskey Stone

Named after a small town in Northern Michigan, the Petoskey stone is the state stone of Michigan. But what is it exactly? And why is it covered with all those hexagons?

A Petoskey stone is fossilized coral, specifically Hexagonaria Percarinata, which dates back to the Denovian period about 350 million years ago. Back then the area that we now know as Michigan was located near the equator. It was a tropical reef where the coral thrived. The species has long been extinct and fossilized and over the millions of years through the process of plate tectonics, this area moved north to its present location near the 45th parallel.

The individual stones themselves were created more recently through glaciation. As glaciers advanced and receded through the region, the sheets of ice carved out the fossils from the bedrock and deposited them across northern Michigan with a high concentration around the Petoskey area.

Rendition of what a living Hexagonaria Percarinata might look like