Petoskey Stone: What It Is & Where to Find It

Petoskey stone is a fossilized coral. It's a unique rock found in Michigan and is Michigan's official state stone. The coral it's made from is called Hexagonaria percarinata and lived in a warm, shallow sea millions of years ago. The stone's distinctive pattern of six-sided "rays of the rising sun" is revealed when it's wet or polished.

What Is Petoskey Stone

The Petoskey stone is a unique and beautiful fossil composed of rugose coral, specifically the species Hexagonaria percarinata. These prehistoric corals thrived in warm, shallow seas roughly 350 million years ago, during the Devonian period. These stones are unique to the Michigan area, particularly around the city of Petoskey. They are commonly found along the shores of Lake Michigan and Lake Huron.

Petoskey Stone. Photo: Smiles7/flickr

Why is it called the Petoskey Stone

The name Petoskey Stone likely came about because it was found and sold as a souvenir from the Petoskey area. The name Petoskey appears to have originated late in the 18th century. Its roots stem from an Ottawa Indian legend.  In 1965, Petoskey stone was named the state stone of Michigan.

What is unique about Petoskey Stones

Several aspects make Petoskey Stones unique and fascinating:

1. Their Distinctive Appearance

Hidden Beauty: Unlike many fossils, Petoskey stones reveal their true beauty when wet or polished. The dry, grey stones transform into captivating displays of six-sided "rays of the rising sun," a pattern unique to the Hexagonaria percarinata coral they originated from.

Natural Artwork: The hexagonal pattern on each stone is a piece of natural artwork, making each stone one-of-a-kind. No two stones have exactly the same pattern, size, or color variations, adding to their individuality.

Rare Coloration: While most are grey, rare "Pink Pets" showcase a mesmerizing pink hue due to iron permeation during fossilization, making them even more unique and sought-after.

2. Their Historical Significance

Window to the Past: Petoskey stones are roughly 350 million years old, offering a tangible connection to Michigan's ancient past and the Devonian period. They remind us of the region's submerged past as a warm, shallow sea teeming with marine life.

State Symbol: Designated as the official state stone of Michigan in 1965, Petoskey stones hold cultural significance and represent the state's unique geological heritage. They are cherished by locals and a popular symbol for Michigan.

3. Their Accessibility

Public Availability: Unlike many fossils, Petoskey stones are relatively easy to find in specific areas along Michigan's shores, making them accessible for anyone to discover and connect with the natural world.

Engaging Activity: Hunting for Petoskey stones can be a fun and rewarding activity for people of all ages, encouraging exploration and appreciation for nature and geology.

Polished Petoskey stone

 

How was the Petoskey stone formed

So, what is a Petoskey stone? It is a fossil colonial coral that lived in the warm Michigan seas during the Devonian time around 350 million years ago. The name Hexagonaria (meaning six sides) percarinata was designated by Dr. Edwin Stumm in 1969 because of his extensive knowledge of fossils. This type of fossil is found only in the rock strata called the Gravel Point Formation. This formation is part of the Traverse Group of the Devonian Age.

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.

During the Devonian time, Michigan was quite different. Geographically, what is now Michigan was near the equator. A warm shallow sea covered the State. This warm, sunny sea was an ideal habitat for marine life. A Devonian reef had sheltered clams, cephalopods, corals, crinoids, trilobites, fish, and many other life forms.

The soft living tissue of the coral was called a polyp. At the center of this was the area where food was taken in, or the mouth. This dark spot, or eye, has been filled with mud of silt that petrified after falling into the openings. Surrounding the openings were tentacles that were used for gathering food and drawing it into the mouth. The living coral that turned into the Petoskey stone thrived on plankton that lived in the warm sea.

Calcite, silica and other minerals have replaced the first elements of each cell. Each separate chamber, then, on each Petoskey stone, was a member of a thriving colony of living corals. For that reason the Petoskey stone is called a colony coral.

Petoskey stone before and after being polished to reveal the intricate details of the fossil coral. Photos by: DevonianCoast

 

Where to Find Petoskey Stone

Petoskey stones can be found on various beaches and inland locations in Michigan, with many of the most popular being those surrounding Petoskey and Charlevoix. The movement of the frozen lake ice acting on the shore during the winters is thought to turn over stones at the shore of Lake Michigan, exposing new Petoskey stones at the water's edge each spring.Petoskey Stones are also commonly found in Iowa, Indiana, Illinois, Ohio, New York, Canada, Germany, England, and even Asia.

Pleistocene glaciers (about two million years ago) plucked Petoskey stones from the bedrock and spread them over Michigan and surrounding areas. This is why Petoskey stones can be found in gravel pits and along beaches far from the Petoskey area.

Specific spots known for their abundance of Petoskey stones:

Petoskey State Park: With two miles of shoreline on Little Traverse Bay, this park is a popular spot for Petoskey stone hunting. You can find both polished stones on the beach and rougher specimens eroding from the bluffs.

Magnus Park City Beach: This park offers 1,000 feet of beach access and is known for its abundance of Petoskey stones, especially after storms.

Bayfront Park & Sunset Park: Located near downtown Petoskey, these parks offer scenic views and Petoskey stone hunting opportunities within walking distance of shops and restaurants.

Harbor Springs: The beaches in Harbor Springs, such as North Beach and Zorn Park, are also good spots for finding Petoskey stones.

Fisherman's Island State Park: This island park offers a unique opportunity to search for Petoskey stones on its shores and explore its natural beauty.

The best time to find the Petoskey stones is early spring after the ice on Grand Traverse Bay has melted along the shore. Each year as the ice is broken up and the winds push the ice in different directions, it pushes a new crop of Petoskey stones towards the shores.

Underwater rocks in Lake Michigan

Tips for Finding Petoskey Stones

• Look for smooth, grey stones: When dry, Petoskey stones may not stand out much. But look for smooth, grey stones that seem to "come alive" with the hexagonal pattern when wet.
• Visit after storms: Storms can churn up the lake and deposit stones on the beach, making them easier to find.
• Explore different areas: Don't just stick to one spot. Walk along the shoreline and explore different areas of the beach to increase your chances of finding Petoskey stones.
• Be patient: Finding Petoskey stones can take some time and effort. Be patient and persistent, and you'll eventually be rewarded with your own piece of Michigan's ancient history.

How to Polish Petoskey Stones by Hand

Petoskey stones are made up of calcite, and therefore are a good candidate for hand polishing. Calcite is soft enough so that it can be easily worked, but dense enough to take a nice polish.

What You Need to Polish the Stones

• Petoskey stone
• Sandpaper (220, 400, or 600 grit)
• A thick towel or newspaper
• A piece of corduroy or velvet
• Polishing powder
• Water

Once you have found the stone you want to polish, sand it down with the 220 the sandpaper mentioned above. After rubbing, rinse the stone down and dry it off. Examine the stone for scratch marks, and if there are any, keep on sanding! All scratch marks should be gone!  Next, sand again with 400 grit sandpaper. This should remove any coarse spots.

Once again, rinse, dry and check.  Now sand the paper with the 600 grit to make sure that the stone is smooth and scratch free. When you think it looks perfect, continue sanding for another 10 minutes, just to make sure.  At this point, it is time to polish. Sprinkle the damp corduroy or velvet with polishing powder. A short, rotating rubbing will polish the stone. However, if scratches appear, start from the beginning with the 220 grit paper to remove them!  When you’re finished with the polishing, simply rinse the stone off in clean water, and dry. Now you have your own, hand polished Petoskey stone!

Due to their unique appearance and historical significance, Petoskey Stones are widely collected and used for jewelry, decorative items, and souvenirs. They are also of interest to paleontologists and geologists studying the ancient marine ecosystems of the Great Lakes region.

Petoskey Stone

What is Petoskey stone used for

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