What is a Petoskey Stone?

My preschooler's class is studying oceans and seas. The first week of class I sent her to school with a chunk of coral to share. This week, I sent her with a petoskey stone, or fossilized coral, that her grandfather had polished for her (usually you can't easily see the pattern on the stone unless it is either wet or polished). I had checked with her teacher first to see if that would be okay, but her teacher had never even heard of Petoskey stones! So I compiled some information for her, and thought I'd share it more generally.

What is a Petoskey Stone?

A Petoskey stone is a rock and a fossil, made of fossilized coral. It is the state stone of Michigan.




Long, long ago, the land that is now Michigan was covered by shallow sea. Coral reefs grew there. Later, the coral was surrounded by stone. During the ice age, glaciers lifted the coral fossil stones from the bedrock, and ground them smooth.

Petoskey stones are often found on the shores of Lake Michigan, one of the five Great Lakes of North America.

Petoskey is an Ottawa term for the rays of light from the rising sun.

Can you see why they might be named that?