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167 Views 11 Replies Last post: Aug 10, 2018 10:13 AM by Colin RSS
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Aug 8, 2018 10:18 PM

Fossil wood?

Hi,

I found this rock (fossil?) on the south coast  of the Isle of Wight.

It is perfectly round, about 7 cm in diameter and very heavy.

Can you tell me if this is fossilised wood or something else?

Regards,

Roufmeister

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    Aug 9, 2018 7:53 PM (in response to Roufmeister)
    Re: Fossil wood?

    Welcome to NaturePlus

     

    Not fossil wood - This looks like FeS2 - iron pyrite from the Chalk (aka "marcasite"). 

     

    Which part of the south coast of the IoW was it?

    Lft Clk to enlarge map

    Capture.JPG

     

    http://www.southampton.ac.uk/~imw/wight.htm

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        Aug 9, 2018 10:41 PM (in response to Roufmeister)
        Re: Fossil wood?

        I agree with Dr T, but it is in the centre of an ammonite but too eroded to even give a genus I'm afraid!

        Please be aware that this will crumble and you will be left with a pile of chalk and a decomposing (rusting) Marcasite nodule!

        Colin

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          Aug 10, 2018 8:28 AM (in response to Colin)
          Re: Fossil wood?

          Can you explain your suggestion of ammonite please Colin?

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            Aug 10, 2018 10:13 AM (in response to Dr T)
            Re: Fossil wood?

            I thought I saw ribs in the second photo, but I'm not so sure now! I think I was wrong - sorry - just a nodule then.

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    Aug 9, 2018 9:50 PM (in response to Roufmeister)
    Re: Fossil wood?

    That makes sense - it may have come from the Chalk capping the adjacent hills - yellowish on the map above. 

     

    Can you clean it up somewhat - it may be a mudstone concretion instead.  Can you weigh it to the nearest gram and measure its volume in ml/cc by displacement in water using a measuring jug or digital scales (http://www.johnbetts-fineminerals.com/jhbnyc/articles/specific_gravity.htm)

     

    Thanks

    Capture.JPG

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    Aug 10, 2018 8:31 AM (in response to Roufmeister)
    Re: Fossil wood?

    That gives a very approx density of 2.8. Any chance you can improve on the volume estimate using the method in the above link?  Pyrite/marcasite is 4.8-5 so you probably have a ferruginous mudstone concretion from the Lower Cretaceous Lower Greensand Ferruginous Sands Formation instead. - photographs are never as good as having the specimen in one's hand! 

     

    Pyrite/marcasite can oxidise to a dull rusty colour and lose the crystal shape and colour but still with a radiating texture - it was this thought and the shape which led us to the first suggestion - hence the need for the additional info. you have provided.

     

    You can find Chale in the Southampton link above by Edit>Find on this Page> Chale

     

    Capture.JPG

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