Mazon Creek Fossil

[Saj]

Hi - I was recently given some concretions from Mazon Creek in Grundy County, IL.  to open.  I have been able to mostly identify some fauna specimens using the Mazon Creek books.  However, not able to identify this one using the book or searches on the internet.  Looks like a gold fish to me.   Any ideas?  

[Darktooth]

@Nimravis may be able to shed some light on this. He has alot of experience with these fossil nodules

[Fossildude19]

Coprolite or mineral staining, would be my guess.
 

[trilobites_are_awesome]

@RCFossils

[Mark Kmiecik]

Tim pretty much called it. Either a coprolite or mineral stain. Most probably mineral stain. There are many "duds" to be encountered when opening Mazon Creek nodules, anywhere from 20% to 90% depending on the location. You would have to examine the specimen with a jeweler's loupe, looking for and finding fragments of undigested organic material to justify calling it a coprolite. This specimen does not have the "typical" coprolite look to it, but it may be one. The two different tones of brown is what makes me lean toward mineral staining.

 

P.S. -- We'd love to see any other specimens that have opened up for you.

 

 

 

Edited December 9, 2023 by Mark Kmiecik
typo

[Saj]

Thanks Tim & Mark! - Here are three others I have from the batch.  

 

@Mark Kmiecik - What do the "fragments of undigested organic material" typically look like?