Need help identifying this rock, Found in northern MN

Rock.jpg
 

Attachments

Last edited:

jim mcnamara

Mentor
3,356
1,574
The image is not visible for me. If you need help getting your image to post, let us know. We can help.
 

berkeman

Mentor
54,308
4,717
@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?
 
@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.
 

Attachments

davenn

Science Advisor
Gold Member
8,296
4,875
The porphyritic basalt seems to be correct. I have been collecting rocks and minerals for 55 years.
 

CWatters

Science Advisor
Homework Helper
Gold Member
10,455
2,264
Cool rock.
 
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:
 

Baluncore

Science Advisor
6,218
1,812
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.
 

gleem

Science Advisor
1,196
626
It looks like what I have known as a "pudding stone"
 

Baluncore

Science Advisor
6,218
1,812
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
 
Does the rock have any value?
 

jim mcnamara

Mentor
3,356
1,574
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.
 

The Physics Forums Way

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving
Top