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548 Views 4 Replies Last post: Oct 18, 2013 9:03 PM by MikeHardman RSS
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Aug 16, 2013 8:10 AM

Strange Marks on a Pebble

Does anyone know what these strange marks are, please?

 

Suggesstions I've had so far are Limpet Marks and a Tubular Fossil.

 

The marks are between 12mm and 15mm in diameter and they are not indented into the rock.

 

Thank you.

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    Oct 18, 2013 6:23 PM (in response to hpcc1234)
    Re: Strange Marks on a Pebble

    Im not an expert but I think that's just where the water has been, or maybe another mineral.

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      Oct 18, 2013 7:56 PM (in response to Dan)
      Re: Strange Marks on a Pebble

      I have looked on the internet about tubular fossils, and I don't think that is one.  If it comes from the sea, that probably made that mark.  The salty waters will probably make all rocks become miscolored on the surfaces over time.  Also it could have collided with another rock when in rough waves and made it.

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        Oct 18, 2013 8:51 PM (in response to Dan)
        Re: Strange Marks on a Pebble

        I Have now looked on the internet about limpet marks, and I'm not sure.  They look similar, but I still think it's a water mark.  Hopefully an expert will give their opinion though.

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    Oct 18, 2013 9:03 PM (in response to hpcc1234)
    Re: Strange Marks on a Pebble

    I take it these are on opposite sides of the same rock...

     

    These have a similarity to a limpet mark, but the mark in the middle needs to be explained too.

     

    It is fundamental to know whether these are just surface markings or whether they go right through the rock.

    Is it possible you could saw the rock in half to test that?

    If so, I suggest you do it carefully so you don't damage the existing marks. You do this entirely at your own risk, but I might suggest using an angle grinder with a stone-grinding blade or a diamond cutting blade. Make sure the rock is firmly clamped (not easy). You could saw just part-way through, then split it with a hammer and chisel (again, take precautions).

     

    If you manage it, and the mark does go right through, my mind is going towards fulgurite - the result of a lightning strike. But even with that, there are several things that are not right. Also, fulgurites are very rarely found.

    If the primary mark/object is in the middle, the halo needs to be explained. It is the sort of thing that occurs in concretionary processes, but even there, it does not feel right.

     

    If the mark is surface-only, another possibility is a seaweed holdfast mark.

     

    Anybody else got some ideas?

    If not, I think this might be one to bring/send to the Angela Marmont Centre for closer inspection!

     

    Mike

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