THE PETOSKY 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.
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.
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.
The picture below illustrates the six sided formation left from the living coral colonies found on the Petoskey stone. These stones are polished and therefore display the fossilization even better. However, the wind and waves and sand cause a polishing effect, and for this reason stones found on the shores of the Bay have a more polished look naturally.
Source: Photograph by Randy Schaetzl, Professor of Geography - Michigan State UniversityHowever, when Petoskey stones are found inland, they are unpolished and therefore less defined.
Where can you find the Petoskey stone?
The Petoskey stone can be found anywhere in the state from the Traverse City
area across the state to Alpena. They can be found in gravel pits, and on road beds.
However, the biggest influx of stones are found on and around Little Traverse Bay, in the
town that gave the stone its name, Petoskey.
HOW TO POLISH PETOSKEY STONES BY HAND
And now for the real fun! 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.
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 youre finished with the polishing, simply rinse the stone off in clean water, and dry. Now you have your own, hand polished Petoskey stone!
This page was created by Emily Teske, a former GEO 333 student. Great job, Emily.
This material has been compiled for educational use only, and may not be reproduced without permission. One copy may be printed for personal use. Please contact Randall Schaetzl (email@example.com) for more information or permissions.