Petoskey Stone: Finding, Identifying, and Collecting Michigan’s Most Storied Fossil

By Dan R. Lynch

Your Definitive Guide to Petoskey Stone

Michigan’s state stone is prized for its beautiful patterning, which is said to resemble the rays of the rising sun. Take an in-depth look at the famous fossilized coral—including a summary of the fascinating natural history, which began 400 million years ago. Learn all about it, and then head out and search for your own.

Get expert advice from author Dan R. Lynch on how to identify and collect Petoskey stones. With tips on where to look and what to look for, along with information about Petoskey lookalikes and other fossils you might find, your rock-hounding trips will be better than ever! Suggestions on what to do with your finds and how much they’re worth add to the knowledge you’ll gain from Petoskey Stone.

From Lake Michigan beaches and Petoskey State Park to gravel pits and riverbeds, grab this book and begin your rock-hunting adventure!

• Language: English
• Publisher: Adventure Publications
• Release date: Feb 19, 2019
• ISBN: 9781591938422

Book preview

PETOSKEY STONES, AND HOW THEY FORMED

Petoskey stones have long been easy to find in Michigan. The Little Traverse Bay, where the highest concentration of Petoskey stones are found, is a beautiful natural area that has drawn in collectors for many years and offered them beautiful water-worn specimens of their own.

But while finding them may be a fairly simple matter, answering the question of what is a Petoskey stone? is a little more complex. With over 400 million years of history, there’s a lot to know about the little hexagons trapped in the rock, and it all starts in the ancient seas of Earth. In this section, we’ll explore the deep history of this enigmatic stone and how it came to be.

Specimen courtesy of Dean Montour

What is Petoskey Stone?

Petoskey within Southern Michigan

Petoskey Stone Is a Fossil Coral

Coral Anatomy

Other Lifeforms in Coral

Hexagonaria and Other Rugose Corals

The Life Story of the Petoskey Stone

Life in the Devonian

Devonian Reefs and Forests

Fatal Algal Blooms

The Late Devonian Extinction

Other Factors in the Extinction

How Old Are Michigan’s Petoskey Stones?

Fossilization

Limestone

The Minerals That Make Up Limestone

How To Identify Limestone

Ice Ages and Glaciers

Petoskey Stones Today

Petoskey Stone Distribution

How Did Petoskey Stone Get Its Name?

Visit Petoskey

WHAT IS PETOSKEY STONE?

Petoskey stone is undoubtedly Michigan’s best known fossil, famous for its enigmatic mosaic-like pattern caused by the remains of an ancient coral species preserved in limestone. It is found most often in the vicinity of the Little Traverse Bay Area, particularly around Charlevoix and the town of Petoskey, from which the stone gets its name, but the popular collectible can be found all across the northern portion of Michigan’s Lower Peninsula.

Until recently, the precise identity of the coral species preserved in Petoskey stone was unclear. For some time, scientists have known that Petoskey stone is a fossil remnant of corals belonging to the genus Hexagonaria, a long-extinct group of corals that developed hexagonal, or six-sided, patterns. These corals thrived in Earth’s shallow seas during the Devonian Period, which started approximately 419 million years ago. But it wasn’t until 1969 that the primary species preserved in the rock was identified as Hexagonaria percarinata, an ancient coral found in rocks in several places in the world, but nowhere as plentiful as in Michigan. Appearing tightly packed together, the hexagonal shapes each represent an individual organism within the once-living coral colony. Each hexagon is segmented, has a gauze-like texture, and often has a central darker spot.

Hexagonaria percarinata, typically shortened to H. percarinata, is a scientific name that will be repeated throughout this book; a coral fossil is only an official Petoskey stone if it contains that specific species. But that distinction isn’t important to every collector, as there are many corals in the Hexagonaria group, and most Hexagonaria fossils from the region share similar patterns and features and formed in the same rock bodies. Instead, to many people, any fossil find is exciting, as they all represent the rich and deep history of life in Michigan and make for beautiful keepsakes.

PETOSKEY WITHIN SOUTHERN MICHIGAN

Most Petoskey stones are found loose in surface gravel or sand; they’re found as weathered, rounded stones. Less weathered specimens appear more ragged and rough, and these better represent the coral as it originally grew.

Petoskey stones are known for their tightly packed, repeating patterns of hexagons. Like most other examples of limestone, they are usually brown, tan, or yellowish, and fairly soft, yet will take a good polish, as shown by this exemplary specimen.

Most Petoskey stones are found on beaches where they have been worn down and smoothed by the wind and waves. These specimens are classic examples of the kind you’ll easily find on the shore. Note how subtle the pattern can be in very worn specimens.

When cut, polished, and viewed under magnification, the complexity of the coral’s shape and structure can be fully appreciated.