Opalescent internal structure peice of ammonite?

[Lone Hunter]

This is rather alien to me compared to what I usually find as far fossils, esp in this creek which is mix of Eagle Ford and little bit of everything. 

Thinking it has to be part of an ammonite but can't visualize it since this is straight and flat. Don't usually see any internal structure so just guessing that's what this is. The colors are awesome, is it nacre or opalized? 

[daves64]

Steinkern of a single section or living chamber (between the sutures) of an ammonite with nacre still present.

Edited June 17, 2021 by daves64

[Lone Hunter]

Very cool thank you! Any idea on the ammonite ID?

[Thomas.Dodson]

9 minutes ago, Lone Hunter said:

Very cool thank you! Any idea on the ammonite ID?

Not going to be identifiable from this.

[DPS Ammonite]

Probably an engonoceritid such as Metengonoceras or Engonoceras since it is very flattened and has a simple suture.

 

See 

 

http://www.thefossilforum.com/index.php?/topic/58593-metengonoceras-or-engonoceras/

 

 and North Texas Fossils (photo of Engonoceras from there: 

 

http://northtexasfossils.com/ammonites.htm