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817 Views 9 Replies Last post: Sep 24, 2013 3:28 PM by MikeHardman RSS
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Sep 20, 2013 1:56 PM

Identification please

Hello everyone,

 

While on a trip to Cow gap 19Sep 2013 (Beachy head) I spotted this in the Gault clay.

 

The pictures do not do it justice. its very hard and appears to be hollow at the wider end (Neck?)

the other end tapers off to a point (tail?)

 

Fantasic fossil and that alone made the 3 hour round trip plus the soaking in the rain worth it.

 

Best regards Pete

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  • Currently Being Moderated
    Sep 20, 2013 3:00 PM (in response to Pete)
    Re: Identification please

    Need Tabfish's experience on this one...

    (smacks of brachiopod to me, but something's not right, or I'm not seeing the photo properly)

     

    Mike

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        Sep 20, 2013 5:50 PM (in response to Pete)
        Re: Identification please

        Pete,

         

        Yes, of course, spot on, well done and thanks for clearing that up.

         

        And it is a bivalve not a brachiopod; I had had in mind this sort of thing.

         

        Mike

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            Sep 20, 2013 9:05 PM (in response to Pete)
            Re: Identification please

            Pete,

             

            Good spot for fossiling.

            Essential reading - http://www.barton.ukfossils.co.uk/ (I expect you knew)

             

            Mike

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                Sep 22, 2013 4:09 PM (in response to Pete)
                Re: Identification please

                Hi Pete,

                 

                Good job. That's come up very nicely!

                 

                In general, living sea shell -type creatures usually have their hard parts made of calcium carbonate, or, much less commonly, calcium phosphate. Calcium carbonate occurs in two forms in these invertebrates: aragonite and calcite. Aragonite becomes less stable as temperature and pressure increase, and since those changes commonly occur during lithification of sediment, agagonite in invertebrate shells alters to a more stable form (calcite) as fossilization occurs. Thus, calcite is a common mineral in fossils, and although aragonate occurs as well, it becomes more unusual in older fossils. During fossilization further changes may occur, such that calcite and/or aragonite and/or calcium phosphate get replaced with silica, haematite, pyrite or other minerals. Sometimes, the original mineral is dissolved and not replaced, leaving a cavity. That can result in fossils existing just as molds, or as casts - where such molds become filled with other material.

                 

                Oyster shells are made of calcite, and that's probably still what your fossil Rastellum is composed of.

                 

                Further reading:

                - http://www.fossilmuseum.net/fossilrecord/fossilization/fossilization.htm

                - http://www.conchsoc.org/interests/fossils.php

                 

                Mike

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