The Petoskey Stone Story
The Petoskey Stone was adopted as the Official State Stone in 1965. A Petoskey Stone is a Tetracoral (Colony Coral): In that many animals lived together in a colony. “Hexagonaria” is it’s scientific name. In each hexagon chamber are the prehistoric remains of salt water marine life. The fossilized coral lived approximately 350 million years ago during the Devonian Age, in the sea which used to cover Michigan.
More specifically the Petoskey Stone is a rock and a fossil, often pebble-shaped, that is composed of a fossilized rugose coral, Hexagonaria percarinata. The stones were formed as a result of glaciation, in which sheets of ice plucked stones from the bedrock, grinding off their rough edges and depositing them in the northwestern (and some in the northeastern) portion of Michigan’s lower peninsula. In those same areas of Michigan, complete fossilized coral colony heads can be found in the source rocks for the Petoskey stones.
Petoskey stones are found in the Gravel Point Formation of the Traverse Group. They are fragments of a coral reef that was originally deposited during the Devonian period. When dry, the stone resembles ordinary limestone but when wet or polished using lapidary techniques, the distinctive mottled pattern of the six-sided coral fossils emerges. It is sometimes made into decorative objects. Other forms of fossilized coral are also found in the same location.
Where To Find Petoskey Stones
You find Petoskey Stones best on overcast or rainy days along the beach (they seem to stand out better on those days). It’s getting harder and harder to find good Petoskey Stones, especially at the popular beaches. To find them in the wild, you’ll have to scour the beaches (Petoskey Stones can be found anywhere in Northern Michigan, but stony Lake Michigan beaches seem to be the best spot to look). If you’re in town, avoid the Bayfront Park, this will be pretty well picked over. Just south, is Magnus Park which might be a good spot to start. Also, if you take 31 South there are several small roadside parks (Bailey’s Place Stones & Stuff is pretty good) between Petoskey and Charlevoix that would be good places to look.