Cystoid or normal geode.

[mighty micraster]

This was found at upper gilwern quarry in wales, UK, which is ordovician marine sediments.

I have heard of ordovician cystoids preserved as geodes, and was wandering if this was one or just a normal small geode.

Measures 3 mm across.

[trilobites_are_awesome]

Normal geode.

[mighty micraster]

Thanks.

[doushantuo]

It's too small to make out details

Cystoid writ large looks like this:

[mighty micraster]

I see now that the shape is different, the diagram is more of a cicle, whereas mine is halfway between circle and oval.

[doushantuo]

The Ordovician of Wales is heavily tectonized.

A lot of fossils don't have their original shape/geometry and proportions anymore.

BTW: this is not the same as me saying this IS a fossil