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465 Views 3 Replies Last post: Apr 4, 2013 8:25 AM by MikeHardman RSS
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Apr 3, 2013 1:59 AM

Red jellybean looking rocks

Hello,

I can find no forum like this in US so I am hoping you can help a girl in New Mexico ID some very interesting rocks that I have found. I've always been something of a rock nut but have never discovered anything like these rocks in 50+ years. If your answer is yes, I can send photos. If no, no harm, no foul. Thank you!

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    Apr 3, 2013 7:23 AM (in response to NewMexicoJeane)
    Re: Red jellybean looking rocks

    Jeane,

     

    There's a good chance we can help you.

     

    Please post photos.

     

    Also, please give us any of this info if you can:

    - location

    - whether loose or in situ

    - whether solitary or just an example from a much larger expanse

    - scale (perhaps in the photo, but otherwise some indication of size)

    - any tests you have done, eg. with a magnet (to test if iron/nickel rich) / with steel (to test if magnetic) / streak (colour can be indicative)

    - this may seem strange, but have you picked it up and shaken it next to your ear? (There is an unusual mineral formation called beekite that often has bean-like pieces containing loose lumps inside;http://www.thefossilforum.com/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=148580. It can have various colours, including red.)

     

    Mike

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      • Currently Being Moderated
        Apr 4, 2013 8:25 AM (in response to NewMexicoJeane)
        Re: Red jellybean looking rocks

        Good info, thanks Jeanne.

         

        I should have been a bit more specific in asking about being in situ or not.

        I'm guessing that by your saying in situ, you mean in recent sediment (not in solid rock, which I intended).

         

        They are pebbles of red quartzite.

        There is a widespread red-pink quartzite called the Sioux quartzite, which extends into north central New Mexico - see http://en.wikipedia.org/wiki/Sioux_Quartzite.

        There is also a brick-red quartzite conglomerate that comprises much of the El Rito Formation

        http://nmgs.nmt.edu/publications/guidebooks/downloads/35/35_p0123_p0128.pdf.

        And other red beds.

        You'd have to look at a geological map of the area to determine the likely source rock.

         

        Whatever rock comprised the source of the material, your pebbles are probably not due to the synsedimentary processes that laid it down. They were probably formed much more recently (few hundred to few million years), as those sedimentary rocks were eroded, and the pieces tumbled and polished in a stream bed or on a lake shore. The linear nature of the occurrence you describe hints at a stream bed, but could be either.

        I say 'probably' because there is a chance your pebbles were formed much longer ago, and redeposited to form a conglomerate (as occurs in the El rito Formation, above). Recent erosion has a propensity to pick-out such old pebbles from a congolmerate, and hence it can be difficult to say at which stage the pebbles were formed (sometimes there are clues, such as preferential pressure solution pebble-to-pebble, but there is none of that in your specimens).

         

        Mike

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