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The Complete Guide to Petoskey Stones

The Complete Guide to Petoskey Stones

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by Bruce Mueller, William H. Wilde

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The Complete Guide to Petoskey Stones is the authoritative guide for everyone who visits northern Michigan and can't wait to comb the beautiful beaches in search of Michigan's official state stone, the Petoskey. This book dispels myths about the Petoskey and reveals the true facts of this ancient fossilized coral. Instructive pictures and maps keep Petoskey


The Complete Guide to Petoskey Stones is the authoritative guide for everyone who visits northern Michigan and can't wait to comb the beautiful beaches in search of Michigan's official state stone, the Petoskey. This book dispels myths about the Petoskey and reveals the true facts of this ancient fossilized coral. Instructive pictures and maps keep Petoskey fans on track every step of the way while guiding them to the best places to find the stone, including those favored by local Petoskey stone hunters and collectors. Once you've found a piece of the prized Michigan fossil, The Complete Guide to Petoskey Stones leads you through the many methods of polishing that bring this beautiful stone to life.

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University of Michigan Press
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5.50(w) x 8.50(h) x (d)

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The Complete Guide to Petoskey Stones

By Bruce Mueller William H. Wilde

The University of Michigan Press

Copyright © 2004 Bruce Mueller and William H. Wilde
All right reserved.

ISBN: 978-0-472-03028-6

Chapter One

Michigan's Official State Stone

In 1965, Michigan Governor George Romney signed House Bill 2297 of 1965, making the Petoskey Michigan's official state stone.

What is a Petoskey?

We must first go back 355-415 million years to the Devonian Period. Devonian is one of the eleven geologic periods that divide the last 545 million years of earth's history, based on the fossil record. The Devonian Period was about 100 million years before the dinosaurs roamed the earth, and Michigan, then positioned near the equator, was completely covered by a warm shallow sea that extended from the Gulf of Mexico through Michigan and into Canada. On the sea bottom were corals, much like the corals you find in the seas and oceans today.

Coral grow by stages. They start out their life as free-floating planulae. The planulae eventually settle on the sea floor and attach to something hard on the sea bottom (polyp stage) where they spend the rest of their life. The coral secretes a calcite "cup like" external covering around itself called an exoskeleton. The soft-bodied coral lives within this exoskeleton and uses its tentacles to collect food.

Some corals, known as rugose corals, live solitary lives, but others are colonial (a group of many with the same characteristics). Hexagonaria percarinatae, the scientific name for the coral whose fossilized remains are known as Petoskey stones, were colonial corals. As the polyp of Hexagonaria grew, it built up a six-sided cup about the size of a six-sided lead pencil. Initially, the cup is short, but in time, it may grow to the length of an ordinary lead pencil. As the polyp grows it produces buds, which become new colony members. These produce their own six-sided cups surrounding the original member of the colony. These buds in turn produce their own buds and in this way, the colony grows. As it continues budding, the colony grows upward and outward and begins, in the typical case, to look like a short-stemmed bouquet of flowers with the founding member of the colony and the early buds having the longest stem-like cups. The top of the colony creates the dome-like look of the flowers in a bouquet. Colonies can grow to one-half ton or larger. Each hexagonal (six-sided) cup is filled with a sunburst of lines that radiate away from the center. The lines, which are actually vertical partitions, are called septa (note radiating septa within the cells as shown in photo on page 13) and are there to provide support and increase the surface area for the soft body of the coral.

Eventually the coral dies. Some die of old age, some from disease, and some are eaten by predators or attacked by parasites. Some also may be buried by underwater landslides called "turbidity currents."

When the colony dies, it is usually buried by mud, and the mud later covered by other sediments. During burial, calcium carbonate precipitates out of solution and fills in the porous areas of the coral. The mud is eventually compressed to form shale, such as the Bell Shale, Antrim Shale, and Ellsworth Shale. (If you place a small Petoskey stone in vinegar and wait overnight, the vinegar will remove the calcium carbonate that has replaced the coral and leaves a white ghost-like remnant of the original exoskeleton which is slightly more acid-resistant.)

These shales form a belt that stretches across the upper quarter of the Lower Peninsula of Michigan, beginning at Lake Huron on the eastern side of the state and going west to Lake Michigan.

Fossil corals, like Hexagonaria, or Petoskey stones, tell us a great deal about their environment. Corals contain algae (a one-celled organism that predominantly lives in water and contains chlorophyll and helps purify the water and air through photosynthesis) that live in their tissues. The algae and corals form a symbiotic relationship, which means they both benefit from each other. The algae take carbon dioxide from the bodies of the corals and return oxygen and elements needed by the corals to live. The algae get a nice safe place to sit in the sun, which they need to live. Because of their symbiotic relation with algae, corals cannot live without sunlight, and sunlight only penetrates water well to a depth of around 200 feet. Therefore, we know that the seas covering what is now Michigan were less than 200 feet deep. Petoskeys thrived where there was an abundance of food, warm water temperatures, and sunlight.

This is how the billions and probably trillions of colonial and rugose corals lived and died in the ancient Michigan Seaway. During a long period of time, they were buried, fossilized, and later brought to the surface by the erosive forces of nature-lakes, rivers, weather, and by the building of roads and other man-made projects that expose them. In the typical case when you find a Michigan Petoskey stone, you do not have a piece of coral, you have a complete coral colony which has eroded intact from a bed of shale.

Why are Petoskeys unique?

Most corals are composed of calcium carbonate (limestone or calcite), they can be and are found in calcareous shale, and can be associated with oil. What makes Petoskeys different that is they belong to the genus Hexagonaria, a Devonian genus that contains many different species.

Here in Michigan the coral's porous insides were filled in by calcium carbonate, making it possible to give the stones a good polish. The corals were invaded at some time by crude oil and it is the oil that gives the stones their "soft" brown color, often with spot-like concentrations of the oil at the center of the cups. It is the amount of crude oil in a stone that determines the lightness (not much crude oil) or darkness (a lot of crude oil) of the stone's color. If you put a Petoskey stone under a black light, it will flouresce blue indicating the presence of crude oil.

Are Petoskeys found only in Michigan?

Most people think that Petoskeys are found only in Michigan. This is not true. They are also found in other Midwest states such as Indiana (Falls of the Ohio State Park located in Clarksville, IN-220 acres of exposed Devonian age fossil beds), Illinois, and Iowa, though certainly the highest concentrations of stones are in northwest corner of lower Michigan.

In Alaska you can find the "Alaskan Petoskey," the "Alaskan Petoskey," however, is a different genus-Xystriphylum.

The Alaskan "Petoskey" is a good example of the fact that even though they aren't really Petoskeys, you can find the same pattern of fossilized corals all around the world where Hexagonaria coral existed some 355-415 million years ago. However, because of calcite infilling, oil coloration, and various preservational factors, Hexagonaria found elsewhere are inferior to Michigan Petoskeys.

It is generally agreed that Petoskeys on the west side of the state are superior to those on the east side, or even the central part of the state, and because of the vast quantities of gravel along the shoreline of Lake Michigan, which are constantly being turned over by the pounding of the waves and winter ice, the Lake Michigan shoreline is the easiest place to hunt for them. A little known fact about Petoskeys and Michigan is that you can even find Petoskeys in the bedrock of the Upper Peninsula of Michigan, though again, your best bet is the Lake Michigan shoreline.

How to find the top of the Petoskey stone

You can find the top and bottom of a Petoskey by looking for the founding member of the colony. The top will look more evenly shaped with the six-sided design, whereas the bottom will often show a more or less centered member with other columns radiating away from it on all sides.

Glaciers and the location of Petoskeys

About 70,000 years ago, the Wisconsin Ice Sheet grew in the vicinity of Hudson Bay and moved toward Michigan. It is thought by some that this ice was about two miles thick, and eventually moved across the Lower Peninsula and carved out the basins of the Great Lakes. The glacier picked up the coral colonies that had weathered to the surface, froze to them, and incorporated them within its body, and carried them south. In the northern quarter of the state it gouged out and freed billions or trillions more from the calcareous shales in which they were entombed. As the glacier moved across the state, it left tremendous numbers of coral colonies scattered across Michigan and undoubtedly carried some into Illinois, Indiana and Iowa. When the ice melted the Petoskeys were left behind as glacial eratics-stones carried by the glacier to places where they don't belong.

Size and shapes of Petoskeys

The glaciers, because of their enormous size and weight, were not gentle with the coral colonies they carried, and these colonies rarely have the outline of a bouquet of flowers. They are much more rounded and are likely to be covered with scratches produced as the glaciers dragged them over the bedrock. There are even examples of "smashed" Petoskeys where the nice 6-sided design is just crushed. These were smashed by the weight of overlying sediments, not by the ice.

As the waves on Lake Michigan and large northern Michigan inland lakes continue to pound their beaches, the Petoskeys tend to be rounded down to the size and shape of an oval bar of soap. Large stones, because of their weight, have a great deal of momentum and each blow sends a series of fractures into the stone to a depth of perhaps an eighth of an inch. Smaller stones have much less momentum and the fracturing barely penetrates the surface.

The shape of stones not found in or near the water are far more irregular and less rounded. This is because they were not subject to the tumbling action of the waves.

Will they ever run out?

Very few new stones are being washed out of the lake and onto the shore each year. Therefore the stones that are already on the beach are the stones that are available to collect. The gravel on the beach is constantly being turned over by the waves, which exposes new stones, but basically the stones that are there are the stones that are available to find. Fresh stones from the lake can be identified by their fuzzy appearance. They have a "rotted" look on the surface and if you sand them down you will find the cause, which is green algae growing within and below the surface of the stone. The new stones that are brought to the beach are brought in not just by waves but with the help of the ice that freezes to the bottom of the lake near shore and brings stones to shore as the ice washes up in the early spring.

There are so many Petoskey stones in the northern Lower Peninsula that it is certain they will never all be collected. Were they all to be collected and put in a pile, we would have a huge pile the size of a mountain. With that said, the easy collecting of the pre-1980s is over. Take enjoyment from finding, not taking.

With this spirit, you will take solace in knowing that most of the remaining stones are not on the beaches, but rather buried in the glacial gravels or in various formations that lie below other layers of sediment.

How to determine the value of Petoskey stones

The value of a Petoskey lies in the perfection of its preservation, its color, the contrast between the color of its various parts and its size. Other things being equal, the larger the stones, the more valuable.

Chapter Two

Rules, Regulations, and Guidelines for Picking Up Petoskeys

"Everyone should be stewards of the land." -Al Ammons, Leelanau State Park Ranger

Rules of the Sleeping Bear National Lakeshore

The rule for the Sleeping Bear National Lakeshore Park, is that you leave the park as you found it. The Boy Scouts have a good rule, too: leave it cleaner than you found it.

Before we get into the official rules about taking Petoskey stones, you must first know what happened to the "Green Stone" (chlorastrolite) on Isle Royal. The Green Stone is the official Michigan state gem stone. Many years ago, they were plentiful everywhere, and then people started taking them off the beaches. Now they are very hard, if not impossible in many areas to find. Let's not let this happen with the Petoskey stone.

The following is from Chris Johnson, Leelanau District Ranger for the National Park Service: The National Lakeshore tolerates individuals taking a stone or two for their personal viewing because of the traditional aspect of the activity, but is very strict about visitors taking quantities of stones of any type from the National Lakeshore.

They have caught people taking stones out in buckets, bags, backpacks and in truckbeds. You won't be happy if you are one of them.

The fines for taking stones out of the National Lakeshore can range from $50 to $5,000 and/or up to six months in jail. However, the high end of any fine or jail time would only be in the most extreme cases, and the ranger would base each decision on the individual case. But be forewarned, the fine for taking stones from the National Lakeshore for commercial purposes will not be light!

Michigan State Park regulations

According to Al Ammons, ranger at the Leelanau State Park, their rules are basically the same as the National Lakeshore's. Officially, their rule is you cannot destroy, damage or remove state property. This includes taking Petoskey stones from the park, though if you are only taking a few for your personal enjoyment, they won't say anything. If you are issued a ticket for taking too many Petoskeys or taking them for business reasons, you can be issued a ticket for a civil infraction and can be given a fine of not more than $500.00.

Property rights-Great Lakes

If you access the beach via a public access and want to get to a spot where you would be crossing a beach area that is private property (you will commonly see signs posted), then you need to be walking in the water to be sure you are within your rights. If you are walking between the water and the ordinary high water mark, be aware that the courts are now determining the private property line, so be safe and stay in the water. There are local customs where people do walk the beach and the owners are accommodating, so make sure you are respectful of what they are allowing you to do. Be quiet, don't walk up close to their homes, leave it cleaner than you found it, and when in doubt, be conservative and stay in the water.

Property rights-inland waters

Inland waters are different than the Great Lakes. You do not have the right to walk in the water or along the shore of a private beach without permission of the property owner.

Property lines and roads

When looking for stones on the side of roads, the first rule is to make sure you get your vehicle safely to the side of the road and leave your flashers on. Be careful. Now for the property line. Typically, county road commissions and the Michigan Department of Transportation (M-DOT) have 66 feet from the center of the road. That's 33 feet from the middle to each side of the road. This can vary from road to road, so to check that you would be on public land, you should call your local road commission or the Traverse City office of M-DOT (231-941-1986). Just like walking the beaches, treat the property and property owner as you would want to be treated if you were the property owner.

Water levels and Petoskey stones

When we wrote this book, the water levels were extremely low, so finding stones in East or West Grand Traverse Bay, Old Mission Peninsula, the tip of the Leelanau Peninsula, and many places along Lake Michigan was much harder because algae was all over the stones. When the water levels rise, the beaches will again start to show fresh, clean stones, with no algae appearing. So watch the water levels and old places might come back as favorite spots.

Where do you find Petoskeys?

Find a beach with plenty of rocks. Sure, everybody knows that, but there are more places to look than just a beach with stones. But before we go there, remember the rules for taking stones out of the National Lakeshore and state parks. You should also remember there are many other interesting stones to find. A great example is the Charlevoix stone, which looks fantastic when polished. There are many stones with patterns that you and your kids can make up names for. Our family has done this and we've come up with names like Saturn rocks (they have rings), Christmas rocks (green and red), and you'll have fun seeing what names you can make up! How about naming one after the kids!


Excerpted from The Complete Guide to Petoskey Stones by Bruce Mueller William H. Wilde Copyright © 2004 by Bruce Mueller and William H. Wilde . Excerpted by permission.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.

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Complete Guide to Petoskey Stones 5 out of 5 based on 0 ratings. 1 reviews.
Anonymous More than 1 year ago
Lots of information on Petoskey stones.