Unknown Fossil

[Harge33]

This was found in a dry portion of creekbed where Devonian age bedrock is out cropped (Lime Creek formation, Mason City, IA).  The fossiliferous layers contain bryozoans, stromatoporids, brachiopods, crinoids.  After using a tooth brush to rid it of the loosest matrix, this is how it looks.  I've attached some microscope pics of the specimen as well. It's essentially a specialized webcam connected via USB to a computer.

 

I'm not able to definitively discern what this is. I'm hoping it's a crinoid calyx but the closest resemblance seems to be some species of oyster.  Any suggestions as to what exactly this is would be most welcome. Thanks

 

 

Sun Dec 18 19-12-48.bmp Sun Dec 18 19-12-48.bmp

[Tidgy's Dad]

It looks like a chert nodule to me. 

[hemipristis]

I agree with @Tidgy's Dad: a suggestive chert nodule.

 

Dont feel bad though, I’m a geologist with 30 years in the field and I still get tricked by those