About Petoskey Stones
Petoskey stones are composed of fossilized skeletons of colony corals which lived their lifespan in the warm sea waters that at one time covered all of what is now the beautiful state of Michigan during ancient Devonian time, some 350 million years ago. Outcrops of these rocks are restricted to the Little Traverse Bay area near Petoskey, Michigan. Glaciers that covered Michigan about two million years ago plucked Petoskey stones as well as many other kinds of rocks and distributed them over Michigan and surrounding areas. Most of the Petoskey stones found along beaches and in gravels have already been rounded and smoothed by glacial and water action. Many of these are suitable for hand polishing and will often take a high polish. Occasionally a Petoskey stone will be found in “rough” form that has not been subjected to smoothing by glacial or wave action. The sample shown above is a fine example of a “rough” Petoskey. It was found in the limestone quarry at Charlevoix. In 1965, it was named the state stone of Michigan.
Petoskey Stone Resources from the Michigan Department of Natural Resources
The Petoskey Stone – Some history, lore and facts about the “Petoskey Stone” (very thorough document)