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Need help with ID on copper nuggets


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I was down in northern Nevada this week for some nugget hunting. All I found were two large, what appears to be, copper nuggets. But, the interior color is more silvery, or gray, than copper-colored. The nuggets I found last fall down there looked like a bright penny on the interior. These two have a black skin on the outside, and when filed away it shows a metallic gray. No attraction to a super magnet. They were both down about 10", and the small one was under a large rock. They were about 300 yards apart in the same drywash. The exposed metal leaves a coppery streak. The black skin leaves a dark gray, or nearly black streak. No way to get a specific gravity...my gem scale doesn't go high enough. Appreciate any help.

On a cheap food scale, they weigh 100 and 71 grams, respectively.

Jim

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Edited by Idaho Jim
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Cuprite?
 

That looks similar to the cuprite I find with a detector.

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9 hours ago, Idaho Jim said:

I was down in northern Nevada this week for some nugget hunting. All I found were two large, what appears to be, copper nuggets. But, the interior color is more silvery, or gray, than copper-colored. The nuggets I found last fall down there looked like a bright penny on the interior. These two have a black skin on the outside, and when filed away it shows a metallic gray. No attraction to a super magnet. They were both down about 10", and the small one was under a large rock. They were about 300 yards apart in the same drywash. The exposed metal leaves a coppery streak. The black skin leaves a dark gray, or nearly black streak. No way to get a specific gravity...my gem scale doesn't go high enough. Appreciate any help.

On a cheap food scale, they weigh 100 and 71 grams, respectively.

Jim

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I'm guessing the first specimen is either bornite or chalcotite. Both are copper sulphides.

Not sure about the second and third. It shows some signs of copper mineralization but doesn't appear to be chalcotite or bornite.

Edited by Morlock
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I'm a little confused with your streak tests. Those alone would help with the identification.

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I appreciate the help, Morlock. All 3 pics are the same specimen. The streak test was done at the spot on the specimen where the metal was exposed with the file. a definite red/brown streak with both specimens. Both specimens are 100% metal, as far as I can tell. They can be scratched with a knife blade, but not easily, so fairly hard. I'll try and get a rough specific gravity later today.

Jim

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8 hours ago, Desertpilot said:

Cuprite?
 

That looks similar to the cuprite I find with a detector.

I'll have to look that up...thanks!

Jim

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The first picture has the typical bluish, purple coloration you'd find on copper sulphides. That was my first impression. I didn't realize the photos were of the same specimen.

Now I'm not sure what you have.

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Cuprite streaks metallic red - brown.

Although Cuprite is dark red it often looks black or dark brown. Look with good magnification for dark red crystals in the matrix.

My guess is Cuprite.

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2 hours ago, clay said:

Cuprite streaks metallic red - brown.

Although Cuprite is dark red it often looks black or dark brown. Look with good magnification for dark red crystals in the matrix.

My guess is Cuprite.

Clay, I poured over these with a USB microscope and can find zero red crystals. Even looked into tiny pockets in the metal...no crystals, red or otherwise.

Really stumped.

Jim

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17 minutes ago, Idaho Jim said:

 

Really stumped.

 

You're not the only one.

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Scanned them with the DFX. Reads 16-28. Wheat penny reads 83.

Jim

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Go outside and hit it with a gas torch. The grey part should turn to copper color under flame. At least the cuprite I find does that. The stuff I find is very similar to what you found. When I get back home I’ll post a pic of the cuprite I find.

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1 hour ago, Desertpilot said:

Go outside and hit it with a gas torch. The grey part should turn to copper color under flame. At least the cuprite I find does that. The stuff I find is very similar to what you found. When I get back home I’ll post a pic of the cuprite I find.

Interesting pic. Cut off a small piece to do an SG test, and the copper is visible in the gray metal.

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1 hour ago, Idaho Jim said:

Interesting pic. Cut off a small piece to do an SG test, and the copper is visible in the gray metal.

 

I'll try that on the small piece I used for the SG test.

Jim

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I heated it to dull red. All it did was melt the copper out of the matrix metal.

JimP6150003.JPG

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17 minutes ago, Idaho Jim said:

I heated it to dull red. All it did was melt the copper out of the matrix metal.

JimP6150003.JPG

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Did you see a green flame?

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Posted (edited)

Morlock, you can't ask a question like that, and then leave me hanging as to why you asked, and what it means...LOL Flame was almost fluorescent green.

Jim

Edited by Idaho Jim
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1 hour ago, Idaho Jim said:

Morlock, you can't ask a question like that, and then leave me hanging as to why you asked, and what it means...LOL Flame was almost fluorescent green.

Jim

I'm sorry. I got carried away doing something else.

The flame test can be used in certain cases to indentify elements in minerals. Since you were going to use a torch on it, I was curious but not surprised by the color of the flame.

https://www.compoundchem.com/2014/02/06/metal-ion-flame-test-colours-chart/

Here's another link.

https://en.wikipedia.org/wiki/Flame_test
Edited by Morlock
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Here is some of my cuprite from AZ. You can see it has a red, grey, or black matrix depending on the location it was found. Some have visible native copper and others don't. All these rocks make my detectors go loco. I live in a area that has large copper deposits so its pretty common to find. Ive also found nugget gold associated with some of these deposits. The gold deposits are epithermal in nature and are on the edges of the larger copper deposits. 

cuprite10.jpg

cuprite9.jpg

cuprite4.jpg

cuprite3.jpg

Edited by Desertpilot
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3 hours ago, Morlock said:

I'm sorry. I got carried away doing something else.

The flame test can be used in certain cases to indentify elements in minerals. Since you were going to use a torch on it, I was curious but not surprised by the color of the flame.


https://www.compoundchem.com/2014/02/06/metal-ion-flame-test-colours-chart/

Here's another link.


https://en.wikipedia.org/wiki/Flame_test

Thanks! I'm guessing from that it was the copper burning off.

Jim

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Posted (edited)
3 hours ago, Desertpilot said:

cuprite8.jpgcuprite7.jpgcuprite6.jpgcuprite5.jpgcuprite1.jpg

cuprite2.jpg

None of those really look like what I found. These nuggets are metal...not mineral. They do have a very thin mineral coating, but under that is metal. The thin coating is black, with here and there some copper oxides, or maybe sulphides. But under all that is metal.

 I like your specimens in any case...especially the next to last. We don't have much like them around here.

Jim

Edited by Idaho Jim
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40 minutes ago, Idaho Jim said:

Thanks! I'm guessing from that it was the copper burning off.

Jim

Yes, it was. It can be used in a lab to indentify elements in a sample.

I've detected and seen many copper nuggets in the past but they don't look like anything that you've found.

 

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