Larry Lyons: Petoskey stone unique to MichiganPublished 9:05am Wednesday, September 23, 2009
Problem is I truly abhor the tedium of striding on treadmills and perching atop stationary bikes. As an alternative I head for the Lake Michigan beach at Bridgman where a couple miles of sand walking and a haul or two up a towering sand dune appease my workout conscience. The other day while walking the beach I came across a gal hunkered down at the water’s edge intently sorting though beach stones. Visions flashed into mind of long ago joyous childhood times I had combing the beaches around Harbor Springs for Petoskey stones.
Mostly just to be friendly I asked her if she’d ever found any Petoskey stones down here. Of course, she hadn’t for they only appear in a small area of northern Michigan.
Most of us Michiganders have at least heard of Petoskey stones but few are aware how unique they are. Petoskey stones are actually fossils of a particular species of ancient coral. Their mottled brown, six sided patterns are somewhat reminiscent of a turtle’s back. The only place in the world that Petoskey stones appear are in six northern Michigan counties, Charlevoix, Cheboygan, Emmett, Presque Isle, Grand Traverse and Alpena.
So what are tropical coral fossils doing way up in northern Michigan, you surely ask? Well, a few hundred million years ago Michigan was at the bottom of a shallow sea way down near the equator. Then earth began rearranging itself. What’s now Michigan was shoved north ending up where it is today. In the process it was also pushed up above sea level. The remains of this unique coral colony were mixed in with limestone bedrock where it fossilized. The only place this limestone bedrock and fossil mixture reaches the earth’s surface is at Little Traverse Bay in northwest Michigan.
About 350 million years ago a glacier wandered by this outcrop, picked up a bunch of limestone and fossils and scattered them across this six county area. Today Petoskey stones are found with some regularity along the beaches, in the sand dunes and inland in gravel pits and road cuts. Nearly all have been naturally ground into rounded rocks and pebbles by glacier and water movement.
In a round-a-bout fashion Petoskey stones get their name from the Ottawa Indian Chief, Petosagay. In 1873 a handful of settlers put down roots on Petosagay’s land. Their translation of Petosagay’s name was Petoskey, which they called their settlement in reverence to the chief. Petoskey grew into a thriving city which is at the heart of the fossil coral area so eventually the fossils were labeled Petoskey stones.
Petoskey stones are composed primarily of the mineral calcite. When the stone is dry the fossil pattern is vague or nonexistent, looking like plain old limestone. When wet or polished, however, the distinctive pattern leaps out. They are quite soft as stones go but just hard enough for many to take a polish. However, some contain enough impurities of other minerals that they won’t polish well or at all. They are one of the few stones that can be shaped and polished by hand with just files, sandpaper and polishing powder. Many are polished in their original shape and set in jewelry but folks of a more artsy bent also carve them into everything from figurines to drawer handles.
Other fossilized coral species occur throughout the Great Lakes region and elsewhere but the Petoskey stone version remains solely unique to the small area of northern Michigan. In 1965 the state legislature officially named the Petoskey stone as Michigan’s state gemstone. We are the only state to adopt a fossil for a state stone.
Larry Lyons writes a weekly outdoor column for Leader Publications. He can be reached at email@example.com