unknown

[Coryander]

Hi,

 

Found this rock containing bivalves in Algarve (Portugal), somewhere between de beaches of 'Praia de Cacela Velha' and 'Praia de Manta Rota'.

 

I broke that rock, and inside is this.

 

Can you please identify it?

Thank you.

 

[fossil_sea_urchin]

I think it's calcite coral or just a nice bit of calcite.

[grandpa]

The second photo looks like a gastropod looking from the top down on the spiral tip.

[Coryander]

Thank you both.

[Mark Kmiecik]

There's definitely some fossil happening there if you look at magnified images of these photos. I can definitely see bivalves, and then a couple of other patterns that look biological. My guess is chunk of reef.

[Oxytropidoceras]

I think that it is a internal mold of a gastropod that has been partially filled with calcite. In addition, the internal mold is further confused by positive casts of wavy borings that animals made into the original shell of the gastropod. For examples of such positive casts, look at:

 

Belaustegui, Z., Domenech, R. and Martinell, J., 2018. An ichnofossil-lagerstätte from the Miocene Vilanova Basin (NE Spain): Taphonomic and Paleoecologic Insights Related to Bioerosion Structures. Palaios, 33(1), pp.16-28.

 

I agree with grandpa, when he stated that the "second photo looks like a gastropod looking from the top down on the spiral tip."

 

Yours,

 

Paul H.