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399 Views 4 Replies Last post: Feb 11, 2014 9:59 AM by Jessica84 RSS
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Feb 11, 2014 5:26 AM

Fossil or rock? (Beach find)

Rock or Fossil?  Found on beach around cliff area Queensland, Australia

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    Feb 11, 2014 5:59 AM (in response to Jessica84)
    Re: Fossil or rock? (Beach find)

    Jessica,

     

    It looks like a piece of mica schist, and from its blackness, the mica is probably biotite. I can see at least two garnet crystals (brownish ovoid faceted lumps). So, if I am right, you could call it a biotite garnet schist.

     

    The pale mineral shown in SAM_0796.JPG could be another mica, muscovite. You will see that it looks somewhat fibrous. That is slightly misleading; that impression arises because the layering (schistosity) is slightly crinkled, causing some of the plates of mica to be seen edge-on.

     

    The pale mineral shown in SAM_0790.JPG is where the rock has broken along a vein, which may be composed of quartz and a greenish mineral (of which there are several possibilities, impossible to tell with microscopic analysis). Schist is a metamorphic rock, ie. it was originally some other rock type, which was subjected to prolonged heat and pressure, causing the original minerals to recrystallize into different ones. The vein could have been present in the original rock, so it, too, was subject to the metamorphism (or some of it, depending on when it arose). That may account for the edges of the vein being indistinct, and the presence of the greenish mineral.

     

    There is a modicum of speculation in my description; microscopic analysis would be needed to be sure.

     

    I wonder where you found the specimen.

    I note that there is a Mica Schist Creek in Queensland...

    http://travelingluck.com/Oceania/Australia/Queensland/_2157933_Mica+Schist+Creek.html

     

    Mike

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        Feb 11, 2014 9:30 AM (in response to Jessica84)
        Re: Fossil or rock? (Beach find)

        Jessie,

         

        Before you visit the NHM, I suggest you call first, to see what facilities/expertise they can offer, which may vary from day to day depending on who is around.

        (I do not work there, so I won't be able to help; I live in Cyprus.)

         

        Mike

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