Petoskey stone is a rock and a fossil, often pebble-shaped, that is composed of a fossilized rugose coral, Hexagonaria percarinata.
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.
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.
|POLISHED Petoskey stone|
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.
Where can you find the Petoskey stone?
|Underwater rocks in Lake Michigan|
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.
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
Read also: What is Sea Glass, and Where Can You Find It?
Wikipedia Petoskey stone