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I just got this one in, and was curious if anyone knows what the black stuff is?

I have had them with manganese and magnetite, but I don't believe this is either... maybe I am wrong.

If there is anything I would have paid more attention to in high school, it would have been geology.

Anyways, thought I would show off this very pretty specimen.

It came from near the American river in California.

Gus-

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Go to someone you know who has a gun and shoot it and see if it could be silver or ...

 

Those guns are accurate and you should know before you sell it.

 

Mitchel

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My guess would be arsenio pyrite.

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Thanks for the comments guys.

Digger, I was actually thinking it could be some form of pyrite, just haven't seen it in this color before.

Wes, Hematite was my second thought.

Gus-

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Digger Bob hit it right... arsenopyrite.

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Gus, The Arseno is supposed to give off a garlic odor when heated with a torch, if you have some extra to test with.

I remember doing that in my minerology class at college.

Imagine 20 students testing various specimens with blowpipes for 2 hours. It was quite the smokefest :lol:

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Years ago, a buddy of mine found a quartz rock that weighed about a hundred pounds in the tailings of a hard rock mine of the Feather River drainage. He hauled it back because his Goldmaster screamed on it. He beat it to pieces with a sledge hammer and inside were small viens of gold and that black stuff, which was later identified as arsenio pyrite. Neither of us had ever seen or heard of it before. He ended up slabbing it and selling it off for some very nice change. The three colors in combination made some beautiful jewelry. He was supposed to save me a piece but not sure if he did. I'd forgotten about it. I'll have to ask next time we go hunting. That's the only reason it looked familiar to me.

 

Digger Bob

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I didn' see this thread before, but Digger and El Dorado are right, its arsenopyrite that has tarnished over time. Freshly broken pieces are more silvery-gray.

See: http://nevada-outbac...ineral_info.htm

I have seen pieces off old CA mine dumps that looked like that your specimen, and arsenopyrite and gold are often associated.

You cant do a density test as it will read too high for gold. The density tests are made for 2 material mixes - gold and quartz. When you add significant amounts of a third, the formulas are totally wrong.

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Big problem with arsenopyrite in slabs for jewelry...it is very brittle

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