Something in flint pebble, any ideas?

[Mahnmut]

Hello dear fellow forum members,

I found this pebble at the north sea coast, quite sure there are fossil structures, but thats as far as I got.

Any ideas? Scale is in cm.

Thanks,

J

Edited November 1, 2023 by Mahnmut
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[TqB]

The elliptical ring looks very much as if it could be a sponge wall.

 

The stripes at the top of the second photo look like a patch of banded flint. That may also be what is filling the sponge cavity, if it is one.