Is this a fossil/hunk of shell fossils?

[himmelangst]

Or just a rock and some shells? Many of the shell imprints are shiny/pearlescent.
Found on Lake Erie shore Erie, Pa.

Thank you!

 

Edited April 2, 2022 by himmelangst

[Tidgy's Dad]

Bits of Devonian brachiopods, I think. 

[himmelangst]

42 minutes ago, Tidgy's Dad said:

Bits of Devonian brachiopods, I think. 

 
Thank you! May I ask what it is called when fossils form in a hunk like this? And why would they still have shell nacre on them? And is that one black area with thicker segmentation a crinoid maybe? Thank you for doing me a learn.

[Fossildude19]

Death assemblage, or hash plate would be the term I would use.

Nacre is sometimes preserved in shell fossils. I'm not sure it is actual nacre, or some mineral replacement that you are seeing there.

Hard to say with the pictures provided, but I don't think it is a crinoid stem.

[Tidgy's Dad]

Well, if there are lots of fossil shells packed together making up most of the rock, then it is known as a coquina, but here I don't think there's enough, so, as the fossils are not in their life positions, I'd call it a death assemblage. The shiny look is not exactly nacre, but a similar looking effect formed from calcite, rather than aragonite which forms true nacre. This is just how some layers of brachiopod shells preserve when fossilized due to the arrangement of the calcite platelets formed in thin layers that refract light in a certain way.

 

Edited April 2, 2022 by Tidgy's Dad

[Tidgy's Dad]

Oh, sorry, it's not a crinoid stem, I think the bit to which you are referring is actually the zig-zag commisure of a rhynchonellid.