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Geology/Possible fossil?


Side of fossil
Side of fossil  

Underside of fossil
Underside of fossil  
Hi there,

My son found what appears to be some sort of fossil in some woods in middle Tennessee. Can you possible tell us what exactly this is? Thank you so much!

Hi Teresa,
Very interesting. You are correct, it is a fossil.  What's called a "horn coral" or "Rugose Coral".  They are still around today but your fossil is probably around 400 million years old.  

Here's a site that will give you a few images and tell you something about them, although it covers corals found in Ohio, the info id the same;

These types of fossils are "colonial" meaning they helped form large reef structures.  They lived in shallow seas.  The flat, wide end with the radiating structure is actually the top.  The structure is made up of gazillions of microscopic critters that settled at one spot, secreted a hard, calcareous shell (with walls and a floor), then proceeded to eat, create little baby corals critters, and then die.  When they died they were either eaten by something else or they deteriorated.  But they left the "house" they built, so other Rugosa settled there, right on top, and made there own house.  In this way you have a small beginning that widens out as the structure grows.

Repeat as necessary and you wind up with a Great Barrier Reef type structure.

Of course reefs are made up of many different kinds of corals; this is just one.  

Another interesting thing about your specimen is the structures seen on the sides of the fossil.  They are not usual for this kind of fossil.  I can only assume there was an odd kind of erosion going on or some atypical growth pattern.  Of course, Geology being the fickle study it is, you may have something entirely different here, but I think my ID is correct.  To be really sure you could take it to your local University or an experienced rock collector.  Holding it in your hand is much better than looking at a photo.

Hope this helps.


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C. Robert Reszka, Jr.


I can answer any general geology question (rocks, minerals, stratigraphy, geomorphology etc.). My expertise is in the geology of the Michigan Basin, PreCambrian, Paleozoic and Recent. I can answer questions concerning mining and petroleum exploration and production and the laws concerning those activities. I can also answer questions concerning stratigraphy of the Michigan Basin. I will also answer questions about mineral and rock collecting in the Basin. I won`t be able to answer many specific questions on hydrology, geophysics or geochemistry. I may be able to answer very general questions in those venues.


I have been working for the State of Michigan for 36 years as a Geologist and a Resource Analyst. I have experience with Subsurface Geology and Petroleum Geology, mining in Michigan, and Sand Dune Mining and Protection issues.

Michigan Basin Geological Society

Decade of North American Geology.
Bedrock Geology of Michigan

BS Wayne State University

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