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Coal with Metallic Inclusion
  
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Stan Feng




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PostPosted: Dec 12, 2017 10:32    Post subject: Coal with Metallic Inclusion  

I recently picked up a piece of coal like rock. I believe it is coal and after giving it some sanding, a metallic layer or inclusion is revealed. It is shiny and silver. However, shortly after exposure to air, a greyish powdery ash started to form on the surface and covered the metallic layer. I tested it with a magnet but it is non-magnetic. I would just like to know is this occurrence common in coal? What actually is the 'metal' or is this a piece of man made material which I have misjudged as coal.


IMG_0002.JPG
 Mineral: Coal
 Dimensions: 6cm
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IMG_0006.JPG
 Mineral: Coal
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kushmeja




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PostPosted: Dec 12, 2017 10:46    Post subject: Re: Coal with Metallic Inclusion  

Hi!

I grew up in Pennsylvania, USA, which is an old coal producing region, and it is relatively common to find pyrite mixed in with some of the coal deposits. Pyrite, especially so from the coal deposits I've seen, have a tendency to degrade rather quickly and break down into silver/white powder with a strong sulfur smell. I'm fairly certain that you have pyrite, but I guess it's also possible that it could be a similar mineral like marcasite as well.
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Bob Harman




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PostPosted: Dec 12, 2017 10:47    Post subject: Re: Coal with Metallic Inclusion  

Pyrite is often found along with coal, but not in the actual coal. I highly doubt that what I am seeing in your photos is coal. Both photos show a faint but definite banding pattern in the part identified as "coal"; looks more like a shale with a pyrite seam (if natural). So first get it properly identified and then go from there. BOB
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James
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PostPosted: Dec 12, 2017 11:16    Post subject: Re: Coal with Metallic Inclusion  

We get pyrite within our coal, either as pyrite nodules or fossils. I have a large pyrite fossil of a cycad cone that came from a coal mine.
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kushmeja




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PostPosted: Dec 12, 2017 11:23    Post subject: Re: Coal with Metallic Inclusion  

Bob Harman wrote:
Pyrite is often found along with coal, but not in the actual coal. I highly doubt that what I am seeing in your photos is coal. Both photos show a faint but definite banding pattern in the part identified as "coal"; looks more like a shale with a pyrite seam (if natural). So first get it properly identified and then go from there. BOB


I've definitely seen and found pyrite seams running throughout coal deposits. From what I can tell from the pics, the specimen in question appears to be coal. It should be rather easy to tell if it is in fact coal - if you scratch it along a brick or piece of concrete, it should easily flake off bits of shiny black dust.
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Bob Harman




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PostPosted: Dec 12, 2017 12:52    Post subject: Re: Coal with Metallic Inclusion  

I guess the pyrite seams and pyrites that I was familiar with occurred adjacent to the coal seams, but I must be wrong on that assumption. As to the basic rock in the photos, I am still not sure it actually is coal. BOB
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Matt_Zukowski
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PostPosted: Dec 12, 2017 21:31    Post subject: Re: Coal with Metallic Inclusion  

Some coal can actually look sort of metallic. The first question i would ask you is how heavy is the specimen? Is it light enough that the whole specimen appears to be coal or is it heavy enough that there is some metallic mineral in it. Second, what is the hardness of the specimen? Can you scratch it with a copper wire? A nail? For more info on trying to figure out what this is, please see "What is this? / Where is it from?"

Good luck.
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Stan Feng




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PostPosted: Dec 13, 2017 06:48    Post subject: Re: Coal with Metallic Inclusion  

Thanks for all your replies. It is valuable knowledge and interesting for me to know all this information. As for the 'coal', I tried rubbing it against paper and it produced black streaks easily and it breaks into tiny shiny flakes as I tried to knock a chip off it. With polishing, it produces a shiny lustre. As for the 'pyrite', the pale gold shiny surface has now turned into a dark grey flaking layer with a powdery feel to it in less than 24 hrs. after I gave it a good sand down and polish.

I have a question on why does pyrite in this occurrence degrade so rapidly as compared to the common cubic pyrite crystals?
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alfredo
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PostPosted: Dec 13, 2017 07:23    Post subject: Re: Coal with Metallic Inclusion  

I would guess you have a very unstable marcasite, not pyrite.
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