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A Tumble Surprise


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Hey Mitchel. It looks like a natural copper nugget to me.  These are two Michigan natural copper nuggets I bought a few years ago and the smaller of the 2 has that same green tinge all over it.   Dave

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7 hours ago, 1515Art said:

I don’t know how they come to be (all smooth and polished) ive seen them by the boxes in gift shops selling nature and holistic Stuff too, shop down by the beach in Capitola sells them.

The same way gold nuggets do... by being washed and tumbled in streams. Copper nugget... I’ve got a jar full of them somewhere that I panned over the years.

Always wanted to go detect here for copper and silver nuggets....

https://pubs.usgs.gov/bul/0448/report.pdf Page 80:

Native copper is associated with silver and gold in the gravels of Chititu and Dan creeks. It occurs in pieces that range in size from fine shot to masses weighing several hundred pounds. Two or three tubs of fine copper are secured at each "clean-up" of the sluice boxes on Chititu Creek and give much difficulty in cleaning the gold, since the finest of the copper has to be removed by hand. Many of the nuggets contain native silver, which shows that the copper and silver are here closely associated in origin. The remarkable similarity in form and appearance between the copper nuggets of the Nizina district and the larger masses of copper taken from the stamp mills of the Lake Superior region is evident to anyone who compares the two, since the chief differences are that the placer copper has a slightly smoother surface and an oxidized coating. The copper and silver are derived wholly or in part from the greenstone. Assays of chalcocite from the Bonanza mine and from other copper ores of the Nizina district have shown the presence of both silver and gold in the copper deposits. Small particles of native silver were found in a freshly broken specimen of greenstone from a bowlder on Chititu Creek, and an assay of the rock also showed its presence. The silver was associated with calcite in small fractures. Silver nuggets up to 7 pounds in weight have been found on Dan and Chititu creeks, but where silver is associated with copper in the same nugget copper predominates, and in general silver is seen only as small particles in the copper. Copper is found only in those tributaries of Dan and Chititu creeks where greenstone pebbles and bowlders form part of the stream gravels; consequently it occurs only where the gravels have been formed in part by streams flowing through greenstone areas or where there is a foreign element in the gravels that Avas derived from a greenstone area and brought to its present position by glacial ice.

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8 hours ago, GB_Amateur said:

Well, maybe it is man-made.  A rock tumbler with abrasives added can wear things down a lot faster than mother nature.

The entire nugget was 'green' when I found it.  The 5 hours in the tumbler gave it some character.  

I also have bought a bit copper nugget from Michigan at the Tucson Gem and Mineral show but it didn't look quite like this.  I also don't remember it being quite so heavy but the GREEN tips it off.

I still don't know where I found it but now I'm thinking desert.

Thanks Rob.

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8 hours ago, mn90403 said:

The entire nugget was 'green' when I found it.  The 5 hours in the tumbler gave it some character.  

I also have bought a bit copper nugget from Michigan at the Tucson Gem and Mineral show but it didn't look quite like this.  I also don't remember it being quite so heavy but the GREEN tips it off.

I still don't know where I found it but now I'm thinking desert.

Mitchel, actually when I said what a tumbler can do, I was thinking if Art was right (well, I thought he was implying manmade, but I might be wrong there), someone previously had tumbled it for much longer than your overnight (or whatever it was) run.

When it comes to geology I'm about as green 😄 as they come.  But it sure looks like a natural find to me.  I actually found a tiny piece myself in glacial till here in Southern Indiana -- in a gold bearing creek.  It's well known that glaciers scoured Canada and the Great Lakes states (e.g. Michigan you mentioned) and left their morraines (and minerals) in the Midwest, so no mystery with mine.

 

 

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The green is what makes this a real copper nugget, not a fake. It’s just a corrosion layer. To build up that thick, it implies the nugget was in the ground for a very long time. Like thousands or tens of thousands of years or more. A man made copper nugget, just like a copper coin, would have no more than a thin green patina.

When I was panning copper nuggets at Dan Creek, it was easy to eyeball them in a gully. You don’t look for copper, you look for bright green nuggets. They stick out like a sore thumb in dark soil.

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