Unusually smooth nodule

[Rockpit]

I found this half of an open nodule last September when I was hunting at Mazonia Braidwood.  It was covered in dirt so I took it home to see if anything would show up when I cleaned it up.  The dirt rinsed off easily and I was surprised to find a layered, smooth surface on the inner half.  The feel and patterns of colors remind me of the inside of a shell.  Has anyone seen this before or have any ideas about what this is?

 

 

[Fossildude19]

Sorry, but I'm not seeing anything fossil related here. 

Just a layered nodule. 

[connorp]

Fairly common occurrence. I tend to have little luck with those finely layered nodules.

[Mark Kmiecik]

No fossil there. A common occurence in some sites where the Mazon Creek concretions are found. The "layered" ones are usually coarse-grained, seldom have any fossils in my experience and when they do they exhibit a relatively poor state of perservation. Most of the time I would leave them behind unless I was nowhere near filling my buckets. That was back in the days when you'd carry two buckets filled above the rim back to the car and have to make two more trips to get the other four buckets. Nowadays I would put them in my bucket and check as many of the layers as possible for fossils.