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184 Views 1 Reply Last post: Oct 20, 2013 12:24 PM by MikeHardman RSS
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Oct 20, 2013 9:55 AM

p

Portobello edinburgh sumarian?neolithic?alien?

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    Oct 20, 2013 12:24 PM (in response to nowayusa2013)
    Re: p

    I don't think it is anything so exciting, certainly not alien.

     

    It is a pebble of concretionary nature.

     

    That is, many rocks contain veins, of one arrangement or another. Where the veins are particularly concentrated and arranged, it may be a concretion of the sort called a septarian concretion or nodule. (There are other concretions that do not have the veining.)

     

    If I am understanding your photos correctly, your particular pebble crosses the contact between two somewhat different fine-grained rock types, probably sedimentary. I suspect the blue side looks bluer in the photo than it really is (?). Veins with a pale blue colour are not common in sedimentary rocks (in metamorphic rocks there are several candidate minerals, such as kyanite). If I had to guess, I would choose celestine.

    See also http://geology.about.com/od/mineral_ident/tp/Blue-Purple-Minerals.htm

     

    Mike

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