Need help identifying this rock, Found in northern MN

  • Thread starter ReevesN76R
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  • #1
Rock.jpg
 

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  • #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.
 
  • #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
@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?
They are embedded.
 

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  • #7
davenn
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The porphyritic basalt seems to be correct. I have been collecting rocks and minerals for 55 years.
 
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  • #9
CWatters
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Cool rock.
 
  • #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:
 
  • #11
Baluncore
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how come you found it in Minesota
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
gleem
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It looks like what I have known as a "pudding stone"
 
  • #14
Baluncore
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It looks like what I have known as a "pudding stone"
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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  • #15
Does the rock have any value?
 
  • #16
jim mcnamara
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As is, not really worth much.

If you like rock cutting and polishing, it would sell for a fair amount after it was polished on a cut through the middle.
Go to a local natural history museum store or one of the places that sell display quality minerals. You can get a good idea. Some mineral collectors use a rock tumbler only to polish. No cut.

My wife did this for fun and the results were amazing.
 
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