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Need help identifying this rock, Found in northern MN

  1. Oct 24, 2018 #1
    Rock.jpg [​IMG]
     
    Last edited: Oct 24, 2018
  2. jcsd
  3. Oct 24, 2018 #2

    jim mcnamara

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    The image is not visible for me. If you need help getting your image to post, let us know. We can help.
     
  4. Oct 24, 2018 #3

    berkeman

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    @jim mcnamara it looks like he was able to upload it now.

    @ReevesN76R -- Welcome to the PF. Can you take a closeup picture of the marks on the rock? Are those marks (like drawn), or are they something embedded?
     
  5. Oct 24, 2018 #4
  6. Oct 24, 2018 #5
    They are embedded.
     

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  7. Oct 25, 2018 #6

    davenn

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  8. Oct 26, 2018 #7

    davenn

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  9. Oct 27, 2018 #8
    The porphyritic basalt seems to be correct. I have been collecting rocks and minerals for 55 years.
     
  10. Oct 27, 2018 #9

    CWatters

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    Cool rock.
     
  11. Oct 27, 2018 #10
    a rhombic porphyry most likely - how come you found it in Minesota, tough? They are more common in the scandinavian region around Oslo, Norway. :wink:
     
  12. Oct 29, 2018 #11

    Baluncore

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    The rock is rounded and river worn, so it was not taken directly from an outcrop. It has probably been carried by a glacier or an ice sheet during the last glacial period. It may have traveled a long way south from some volcanics in Canada.
    I have found identifiable rocks in unexpected places, but only where glaciation was available to transport them.
     
  13. Oct 29, 2018 #12

    256bits

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  14. Oct 29, 2018 #13
    It looks like what I have known as a "pudding stone"
     
  15. Oct 29, 2018 #14

    Baluncore

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    Pudding stone is a sedimentary "conglomerate" of rounded pebbles in a fine matrix. It looks like a cut slice through a plum pudding.

    The rock pictured was volcanic, having a fine green basalt matrix with large phenocrysts of feldspar. A rock with phenocrysts is described as a porphyry, or as being porphyritic. The phenocrysts are crystallised out of the melt over many years as the magma gradually rises up towards a volcanic vent. The fine grained matrix indicates that it cooled quickly once it reached the surface which is why it is known to be a volcanic rock.
    https://en.wikipedia.org/wiki/Phenocrysts
     
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