So, i found a weird structure in a piece of jurassic limestone. It is cylindrical and roughly one cm in diameter, enters the stone on one side and leaves on the other. Under the microscope, you can see particles of limestone/calcite at the inner walls, partially being held in place by some hair-like fibers. Is this a fossil, and if yes, what kind of animal or plant could this have been? Or is it something anorganic?

I'm new here, please tell me if i forgot to mention anything important. Thanks in advance.

Here are some pictures: enter image description here

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  • $\begingroup$ Hi it is hard to tell only from pictures! It is possible to be something fossil however it also can be some mineral structures $\endgroup$
    – Weiss
    Jul 20, 2022 at 12:16
  • $\begingroup$ What could I do to identify it or what further information would be needed for that? I've found these things a few times now and am really wondering what it is. $\endgroup$ Jul 20, 2022 at 12:49
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    $\begingroup$ To downvoter: why -1? Fossil identification questions are perfectly on topic here. User provided info on location, photos... A comment explaining what could be improved would have been nice... $\endgroup$ Jul 20, 2022 at 13:25
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    $\begingroup$ I'm impressed, this is the first time anyone has provided pictures via a microscope. Having such a picture of the fibrous material would have been good. My question about the fibrous material is, is it hard or soft, does it break easily? My two thoughts are it might be asbestos or it could be a tree root that has made its way deep into the limestone via cracks within the limestone. However, I'm puzzled by the two brown/reddish rings, the first immediately around the perimeter of the hole & the second some distance from the hole. This might be iron staining associated with the fibrous material. $\endgroup$
    – Fred
    Jul 20, 2022 at 17:43
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    $\begingroup$ I justed tested it, the fibers are soft. Upon contact with a needle, the whole structure moved but didn't break, almost like a spider Web. That means it's probably not fossil-old, right? Also, regarding the rings: This coloring of the stone is not unusual there, but it normally is even, this ring-form is unusual. There are, however, some pieces where there is a layer of the red substance between limestone and some calcite crystals. Under the microscope, it has a sponge-like structure, the surface dotted with calcite and some black crystals. $\endgroup$ Jul 20, 2022 at 18:29

1 Answer 1


It is a chemical concretion. the shape and structure are a common form of concretion. there may be a tiny flake of fossil that acted as a seed for chemical deposition but this could be microscopic or long dissolved. the fibers are likely bacterial.

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  • $\begingroup$ Thanks! I've read a part of the article and a few Wikipedia articles and think I kind of understand it. But what do you mean with "the fibers are bacterial"? Are they fossils of bacteria or a more recent bacterial phenomenon? $\endgroup$ Jul 23, 2022 at 14:18
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    $\begingroup$ thes fibers are recent bacterial $\endgroup$
    – Weiss
    Jul 24, 2022 at 7:14
  • $\begingroup$ Thanks for your help everybody! $\endgroup$ Jul 24, 2022 at 11:09

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