Opalised pipi shell with periostracum?

[Vopros]

This is a shell from Lightning Ridge, Australia. It had something on it. Is this periostracum? 
if so how was it preserved in 3D. All images but the first one were taken under a microscope.

Thanks!

 

[Ludwigia]

I think you'd need to get some chemical tests done on that in order to determine the answer to your question.

[Coco]

I doubt very much that the periostracum of a shell can be fossilized because it is made of a very fine and organic material. I’m thinking more of a mineral that developed there.

 

Coco

Edited December 9, 2023 by Coco