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Author Topic: Can anyone Identify this?  (Read 40227 times)

Offline AndrewJ

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Can anyone Identify this?
« on: 16/02/2008 20:52:30 »
I found this rock while doing yard work about 3 years ago at my grandmothers house, it was found underneath an embankment by a river. I brought it to my local university and they were stumped as to what it is. Ideas anyone? (sorry for bad quality, need new camera)

1.a dark green color
2.some "melted" areas where the rock is shiny ans smooth
3.various crevaces
4.a strange tan substance growing on it that is able to be scratched off to reveal the original green color.
5.about the size of my fist, heavy for it's size

Pics:




 

Offline JimBob

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« Reply #1 on: 16/02/2008 21:04:32 »
First, Andrew, thanks for joining the forum - welcome.

Second - where do you live? How hard is the green stuff? Can you scratch it with a fingernail, a iron nail or not. Are there any flat planes one the green stuff that makes regular angles that are repeatedly? If so, it is some sort of crystal.

Also, what does the tan rock seem like? is is just a crust or is it an all around the green rock?

My first impression is that it might be olivine BUT that is just an impression, not at all a certainty.
 

Offline AndrewJ

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Can anyone Identify this?
« Reply #2 on: 16/02/2008 21:11:05 »
Umm, I live in Connecicut, United States, and i cant scratch it with my fingernail, but i can with an iron one. there are some flat spots, but they dont repeat, and the tan is like a crust. Thanks alot for checking it out, its getting fruturateing looking for it on google.
 

paul.fr

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Can anyone Identify this?
« Reply #3 on: 16/02/2008 22:15:57 »
was it found anywhere near lime rock park?  [^]
 

Offline AndrewJ

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« Reply #4 on: 16/02/2008 22:19:08 »
Nope, in my grandmothers backyard =]
 

Offline turnipsock

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Can anyone Identify this?
« Reply #5 on: 16/02/2008 22:23:44 »
Looks like melted glass. Does that cork have anything to do with it?

Is it metalic in any way?

 

Offline AndrewJ

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Can anyone Identify this?
« Reply #6 on: 16/02/2008 22:37:46 »
Umm no ha ha the cork is for scale, and the no its not metallic
 

Offline JimBob

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Can anyone Identify this?
« Reply #7 on: 17/02/2008 00:31:09 »
The Heartford Basin, which is only about 20 miles wide at its widest point and which extends north-south through the state is the only place where there are sedimentary rocks in Connecticut and even there there are basalt flows that have been folded into the sedimentary rocks. The rest of the state is either gneiss or schist (metamorphic rock types) and other igneous basalts.

So, I am going to stick with the Olivine for the moment. Our hard rock geologist is on a consulting job and I am the only other who posts regularly and I am NOT an expert on hard rocks. Bass will bee back soon so check back in a few days to see if he has any other ideas.

Jim
 

Offline AndrewJ

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« Reply #8 on: 17/02/2008 00:33:39 »
thanks so much for your help jimbob, i really appreciate it!
 

Offline frethack

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« Reply #9 on: 17/02/2008 09:19:03 »
Is it possible to get a clear close up of the texture? (both the rock and the tan stuff if possible)
« Last Edit: 17/02/2008 09:20:35 by frethack »
 

Offline Bass

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Can anyone Identify this?
« Reply #10 on: 18/02/2008 00:54:19 »
Welcome to the forum! 

Looks like it may contain quartz fragments?



Like fretback, I would love to see a clearer image.  Olivene is a definite possiblility, but large masses of olivene like this are rare- usually restricted to ultramafic rocks.  Other green possibilities are hornblende/augite (amphibole family) or any number of calc-silicate (skarn) rocks. 

Does this green scratch easily with a knife?  You meantioned it seemed heavy, how does it compare to similar sized "garden variety" rocks- twice as heavy? a bit heavier?

Can you do a streak test? (sorry, Neil, this doesn't involve running naked through a futball match- don't want to get ewe all excited)  Scratch the green on some rough porcelain- what color streak does it leave?

Any micaceous minerals?

When it breaks, does it leave straight, smooth surfaces, or does it break in curved (conchoidal) surfaces like glass?  Are there any minerals in the crevices?
« Last Edit: 18/02/2008 00:56:35 by Bass »
 

Offline AndrewJ

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« Reply #11 on: 18/02/2008 01:23:11 »
Sorry for late reply, havent been around all day. The rock is scratched easily with a knife, and is about twice as heavy as a normal rock of the same size. It does not break like glass, more of a smooth surface, i dont have any rough porcelain on me at the moment but i will get back to you on that. And to answer your question on the minerals, there were some debris in the crevaces, but no other form of rock. The quarts i have no clue about (not experienced)
« Last Edit: 18/02/2008 01:24:42 by AndrewJ »
 

Offline Bass

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« Reply #12 on: 18/02/2008 01:31:43 »
AndrewJ, are the white white areas that I circled harder or softer than a knife?
 

Offline JimBob

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« Reply #13 on: 18/02/2008 04:07:17 »
Bass,

Look at the map at http://www.wesleyan.edu/ctgeology/images/CtGeoMap_big.jpg There could be a lot of ultra-mafic basalts in the Hartford Basin. These are rift faulting related basalts with dolerite. I did consider amphiboles and still do. It looks to me like something injected into sedimentary rocks. That is why I was going with the olivine since it will scratch with a iron nail. Even amphibloles, except for stuff like talc are not often found in large chunks like this, are they?

How was your trip? - PM or email OK. Also see advertising section of Oil and Gas Journal for this week, 2/17/08.
« Last Edit: 18/02/2008 04:11:37 by JimBob »
 

Offline DoctorBeaver

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« Reply #14 on: 18/02/2008 07:55:44 »
Our hard rock geologist is on a consulting job...

Does he have anything to do with Metallic Ore?

(think about it)
 

Offline Bass

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« Reply #15 on: 18/02/2008 17:47:59 »
Our hard rock geologist is on a consulting job...

Does he have anything to do with Metallic Ore?

(think about it)

 

Offline Bass

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« Reply #16 on: 18/02/2008 17:50:19 »
AndrewJ, where in CT did you find this (where does your grandmother live)?
 

Offline AndrewJ

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« Reply #17 on: 20/02/2008 21:17:35 »
Umm, my grandmother lives in a rural part of Connecticut called Sterling, not many people know where it is.
 

Offline Bass

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« Reply #18 on: 20/02/2008 23:10:08 »
The Preston Gabbro (ultramafic rocks containing dunites and pyroxenites) is somewhat south of Sterling (I think the local Indian tribe built a casino on it).  Has been explored for copper, nickel and platinum over the years.

Any chance you could send me the specimen (or a piece of it)?  Would love to have a look at it and then send it back.  Will email my address.
 

Offline Professor Gaarder

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« Reply #19 on: 24/02/2008 14:10:03 »
the brown rock on the outside is probably just some kind of silicate . . . the look says it's jade, and had it been found anywhere else I would probably say that. but connecticuit? I doubt it. also, definitely not turquoise. it's a tricky specimen . . . I almost feel guilty asking this of you, but have you tried certain acids on it? Hydrochloric Acid, perhaps?

If the brown part starts fizzing real sharp on contact with the acid, the crust has magnesium in it. The rock itself won't do anything, most stones are just silicon dioxide (sand/natural glass)
 

Offline Professor Gaarder

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« Reply #20 on: 24/02/2008 14:16:45 »
I highly doubt that it's basalt, but no idea about the amphiboles.
 

Offline Bored chemist

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« Reply #21 on: 24/02/2008 18:01:36 »
"If the brown part starts fizzing real sharp on contact with the acid, the crust has magnesium in it."
What?
Limestone fizzes nicely with acid, and doesn't have any Mg in it.
 

Offline JimBob

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« Reply #22 on: 24/02/2008 19:50:01 »
Obviously, Prof., you don't know much about geochemistry. Ultramafic rocks, such as those in CT can form olivine easily. The eastern part of CT where the specimen was found contains dunites and gabbros - rocks that were formed from ultramafic intrusive igneous rocks, in which the mineral differentiation has a long time to take place as the intrusive rock cools over time.

If the Browm matric fizzes in HCL it is most likely the presence of a carbonate - something I do not even consider in this case. Mg has no such properties.

The rock itself won't do anything, most stones are just silicon dioxide (sand/natural glass)


Absolutely wrong. There is an abundance of carbonates and complex silicates in the geologic sequence as well. Pure silica is not as common as you might think.
 

Offline Professor Gaarder

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« Reply #23 on: 25/02/2008 00:48:44 »
Magnesium dissolves completely in hydrochloric acid. It forms a common salt known as Magnesium Chloride.

I've watched it happen.

But I have another theory. I just took out an old piece of fancy jasper, and while it is slightly darker than your specimen, it has the same quartz-like areas and greenish tinge.
 

Offline Professor Gaarder

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« Reply #24 on: 25/02/2008 00:50:30 »
and after a breif google image search, I'm going to guess it's not olivine.
 

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« Reply #24 on: 25/02/2008 00:50:30 »

 

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