Petoskey Stones – fossilized coral

While in Michigan, Rich and I have discovered rock hunting.  I never realized how many ocean fossils have turned into rocks.  I am hooked and Richard is a friend for the big ones.  One of his favorites is the Petoskey stone.

A Petoskey stone is a rock and a fossil, often pebble-shaped, that is composed of a fossilized rugose coral.  These 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.  We call these mushrooms and Rich has some enormous worth over $500 Each.

The Petoskey stone is Michigan’s s state stone.  It is named after chief Petosega of the Ottawa Indian Tribe.  The stone are not very amazing when dry unless they have been polished.


When you sand them down and polish them up, they are gorgeous.

10615957_693768544050912_7416231852299096766_nHexagonaria Percinata is tightly formed six sided, corallites.  These are the skeletal remains of the coral polyps.  The center if each polyp was the mouth that had little tentacles that were always searching for food.  This is a picture of what it looked similar to when alive millions of years ago.


Petoskey stones are found in the Gravel Point Formation of the Traverse Group. They are fragments of a coral reef that was originally deposited during the Devonian period.   We have found them on land and in the water.  The smaller stones are easier to spot if they have been tumbled over other rocks.  You can notice the markings more.

I will post more on how to find them.  How to clean them and what to do with them.

Some slab petoskey stones a friend of ours uses in mirrors and frames.10624971_558907867569059_1187709491858387045_n

Richard cle‌aning rocks


About daniellesdives

diving enthusiast
This entry was posted in Uncategorized. Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s