Is This Coprolite?

[twilight.amoeba]

I recently found this whilst scouring the beach at Gileston, South Wales, UK.

The foreshore at Gileston is full of Jurassic Boulders, I find that many of these contain shells and ammonites. There are hundreds of Gryphaea by the shore too.

However, I found something very unusual today:

It is so bizarrely realistic I first thought it was a hoax or piece of tired dog poo, but then I realised it's made of stone.

Any help identifying this is greatly appreciated!

[Metopocetus]

Those would be molds from shells. The matrix hardened and the shell disappeared...leaving you with what you have there.

[Bill]

Hi,

Do we call you twilight or amoeba

It's an internal cast of a Gastropod, without the shell, which would have had/or not, some kind of ornamentation, it is nigh impossible to id.

[twilight.amoeba]

Those would be molds from shells. The matrix hardened and the shell disappeared...leaving you with what you have there.

Oh, that's fascinating! Thanks!. Still really looks like a poo though

[twilight.amoeba]

Hi,

Do we call you twilight or amoeba

It's an internal cast of a Gastropod, without the shell, which would have had/or not, some kind of ornamentation, it is nigh impossible to id.

Thanks very much for replying. Do you know why there seems to be some sort of different mineral in-between the swirls?

I think its fascinating that an internal cast could survive.

Twilight or Amoeba is fine.

[Bill]

It looks like there may be decaying, (rusty), Pyrite on the specimen. Pyrite is quite common on/in fossils. The internal cast is caused by the shell getting filled with mud, clay etc which in turn hardens. The shell may have been dissolved by sulphuric acid, a by-product of the decaying Pyrite, which was in and around the original shell. Abrasion caused by wave action/gravel/sand, can also remove the softer shell.

[Guest solius symbiosus]

A lot of molluscs secrete aragonite; which is an unstable polymorph of CaCO3. Hence, the dissolution of shell material.