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2673 Views 4 Replies Last post: Jul 1, 2014 10:10 PM by Davidson RSS
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Jul 1, 2014 7:29 PM

Can You Help Identify This Rock?

My son found this rock on a beach in Wales. It was dark grey with a line of white running through it. He decided to crack it open and found in a couple of the small pieces with the white crystal were purple and pink quartz/crystal along with flecks of gold looking pieces. The dark grey stone does not seem to scratch glass but will easily mark wood and plastic. Can you help us identify what we have?DSC_2623.JPGDSC_2575.JPGDSC_2572.JPGDSC_2629.JPGDSC_2633.JPG

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  • Currently Being Moderated
    Jul 1, 2014 8:42 PM (in response to Davidson)
    Re: Can You Help Identify This Rock?

    The fine-grained nature of the host rock makes it difficult to ID from photos of hand specimens (really need to inspect a thin-section under a petrological microscope).

    However, (yes) the white/pastel mineral is quartz, and the golden speck is a piece of pyrite (iron sulphide).

    The quartz and pyrite are part of what was a vein. Such veins can occur in many types of rock: they do help with the ID of the rock itself.


    If you give me the exact location, and if the rock is representative of the bedrock at that spot, I may be able to tell you more by consulting a geological map.



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      • Currently Being Moderated
        Jul 1, 2014 9:51 PM (in response to Davidson)
        Re: Can You Help Identify This Rock?

        The bedrock there is Permian sedimentary rocks of various sorts. If your piece came from such a local source, it might be a siltstone, albeit a bit massive (unlaminated) and siliceous (judging by the way it fractures). But if it was loose on the beach, there's a good chance it came from further afield, brought in by glaciers and/or rivers. In that case it could be a metasediment - a slightly metamorphosed siltstone perhaps. A fine grained intermediate volcanic rock is also possible (not quite dark enough for a basalt (chemically basic)).



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