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Author Topic: Help to Identify a Rock  (Read 8203 times)

Offline LeeAnn

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Help to Identify a Rock
« on: 26/04/2009 03:02:47 »
I was on the beach looking for shells and rocks this past Friday and I came upon what looked to be a greenish looking rock, especially when I saw it wet under the water.  I was wondering what kind of rock it was.  I have attached some pictures and one of the pictures, put water on the rock to make it wet.  It has a white streak running straight through it. Thank you for the help!


 

Offline LeeAnn

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Help to Identify a Rock
« Reply #1 on: 26/04/2009 03:05:04 »
I am hoping the remaining images are now showing.
 

Offline LeeAnn

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Help to Identify a Rock
« Reply #2 on: 26/04/2009 03:06:52 »
3rd Pic
 

Offline LeeAnn

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Help to Identify a Rock
« Reply #3 on: 26/04/2009 03:07:52 »
4th Pic (final)
 

Offline Bass

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Help to Identify a Rock
« Reply #4 on: 26/04/2009 05:07:53 »
From the photos, I suspect the dark green is amphibolite.  (amphibolites are metamorphosed mafic lavas- basalt or andesite).  White streak is a quartz vein.  Pink is a crayola crayon (just wanted to impress you with my powers of observation) ::)

Welcome to the forum!
 

Offline LeeAnn

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Help to Identify a Rock
« Reply #5 on: 26/04/2009 06:35:50 »
You definitely are observant!  ;)
Thank you for your reply. It was such a cool green color. I had tried to find a green rock and could only find dunite, but it did not look like that kind of green.
Glad for the help!  :)
 

Offline Bass

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Help to Identify a Rock
« Reply #6 on: 26/04/2009 07:11:37 »
If you can give me the region where you found this, it'll help to be more definitive.
 

Offline LeeAnn

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Help to Identify a Rock
« Reply #7 on: 26/04/2009 18:48:17 »
It was found on Hampton Beach in New Hampshire.
 

Offline JimBob

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Help to Identify a Rock
« Reply #8 on: 26/04/2009 20:04:37 »
A Schist! It probably came from an exposure of bedrock such as this from Pemaquid Point, Maine. It is an outcrop of metamorphic schist that we originally sedimentary rocks -  alternating sand and shale layers.


 

Offline Bass

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Help to Identify a Rock
« Reply #9 on: 26/04/2009 23:04:08 »
A Schist! It probably came from an exposure of bedrock such as this from Pemaquid Point, Maine. It is an outcrop of metamorphic schist that we originally sedimentary rocks -  alternating sand and shale layers.

WOW! a fine-grained schist with no foliation :o (what'll they think of next?)

Schist: n.   Any of various medium-grained to coarse-grained metamorphic rocks composed of laminated, often flaky parallel layers of chiefly micaceous minerals

Might be slate- but certainly not schist.  Boar's Head, just north of Hampton Beach, is a glacial deposit (probably a drumlin)- so your specimen could have been transported from up to 100 miles away.  There is all sorts of metamorphic bedrock north of Hampton Beach in southern NH, including metabasalts (amphibolites).  I stick by my original answer.
 

Offline LeeAnn

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Help to Identify a Rock
« Reply #10 on: 27/04/2009 03:47:45 »
Bass and JimBob,
Thank you for your replies. They have provided much information for thought. It has been a rock learning weekend. Thank you for that.
Since the rock is so smooth, worn down from oceantumbling, it does not necessary look like too many of the schist pictures that I have been able to bring up. The shist appears to be more "speckily" and my specimen has more lines. But it could just be the ocean wear on the rock. I rather like the white quartz vein myself. It is nice contrast.
The rock is definitely a keeper for me.  :)
 

Offline JimBob

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« Reply #11 on: 27/04/2009 05:12:13 »
The wear is due to the rock being tumbled against each other in a river and then in the surf. it knocks all the edges and highpoints of until there is a smooth surface. If you look closely at the greenish part it will small crystals in ti. But since they haven't had time to really grow, i.e., been under my pressure and temperature, they are still very small.
 

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Help to Identify a Rock
« Reply #11 on: 27/04/2009 05:12:13 »

 

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