With a few weeks left until fall weather makes beachcombing uncomfortable, many are out along northern Michigan beaches looking for Petoskey stones.
But people often find Charlevoix stones, which look very similar to those who are experienced in telling the two coral fossils apart.
Both types of stone are fossilized corals that are about 350 million years old, according to Visit Charlevoix.
The Charlevoix stone, although similar in appearance to its cousin, has its own unique features and structure.
Here’s what to know about Petoskey and Charlevoix stones, and where you can find them in Michigan:
How can you tell Petoskey and Charlevoix stones apart?
Both stones are shades of gray and beige, and are found in the northern part of the state. Petoskey and Charlevoix stones are both are different species of coral. It’s not uncommon to find both fossils while exploring area beaches.
Petoskey and Charlevoix stones are fossilized coral that is about 350 million years. The coral grew during the Devonian Age.
Petoskey and Charlevoix stones are made up of hexagonaria percarinata which consists of tightly packed, six-sided corallites — the skeletons of the once-living polyps. Because they are similar corals, both Petoskey and Charlevoix stones have a honeycomb appearance.
At the center of each coral polyp was the mouth that contained tentacles that reached out for food. The hexagon shape of each cell and thin lines radiating out from the dark “eye” in the center are distinguishing features unique to the Petoskey stone, according to Visit Charlevoix.
The Charlevoix stone has a smaller exoskeleton compared to its cousin the Petoskey stone. The Charlevoix stone is a favosite which has a smaller pattern and a lighter or white color set of small rays radiating from the eye forming the characteristic hexagonal shape which are lighter and they don’t always attach to the center dot, Visit Charlevoix explains.
How do I know if I have a Petoskey stone?
You have a Petoskey stone when the appearance is symmetrical and honeycomb like. Additionally, the fossil has deep lines.
How do I know if I have a Charlevoix stone?
You have a Charlevoix stone when the specks on the stone are frequent and are inconsistent.
Charlevoix stones in some cases, are duller than a Petoskey stone.
The easiest way to tell the difference is that Charlevoix stones have a smaller hexagonal exoskeleton pattern compared to Petoskey stones.
How Petoskey and Charlevoix stones formed
Michigan once was covered by an ancient saltwater sea. As seas became shallower, sand and dirt covered corals. Coral skeletons hardened into stone over time, according to the Torch Conservation Center.
When did the Petoskey stone become the state stone?
On June 28, 1965, then-Gov. George Romney signed a bill making the Petoskey stone the official state stone, according to the MEDQ.
Is there a limit on how many rocks a person can collect?
According to the EGLE, one person can not exceed 25 pounds per year on state-owned and public trust lands.
Jalen Williams is a trending reporter at the Detroit Free Press. Contact him at jawilliams1@freepress.com.
This article originally appeared on Detroit Free Press: Petoskey, Charlevoix stones turn up on Michigan beaches. How to tell them apart
Reporting by Jalen Williams, Detroit Free Press / Detroit Free Press
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