Help identify this rock

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I found a rock next to some railroad tracks by south tunnel. It is light weight, 17g I figured the density to be about 2.36 g/cm3. It is a shiny metallic silver, jagged shaped with no noticeable pattern. It will break or shatter into little shards of no particular shape, and is still silver inside. It has some occasional tiny round holes big enough to poke the tip of a pin in I can find nothing about it online except for a similar story of someone finding it by tracks also in the TN/KY area. I remember reading a book showing the process of coal formation from organic matter to dirt, to darker and darker matte looking rocks, to shinier and becoming more silver looking until it looks like this, but I have not found that stuff on line. Wikipedia says the latest stage of coal is graphite which is "hard to ignite" I didn't know it would burn. This stuff seems to be well beyond graphite and glows a bright red when heated with a propane torch, but no burning like anthracite. I'd post a picture if I knew how to use this site.

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Type: Question • Score: 3 • Views: 1,897 • Replies: 12

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@Nutball,

To post a picture, assuming you have it saved on a photobucket type site:
Open the BBCode Editor above the message box and click on [img]. Then paste your image url within. If the BBCode Editor does not appear, use [img] [/img] instead.

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@Nutball,

A chunk of Mica maybe? We really need a photo.

To post a photo on this site all you really need to do is upload the photo to a standard internet photo site somewhere and then provide us a link to it.

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@rosborne979,

Definitely not mica as I know it, it doesn't shatter in layers anyway. Pics on this link:

http://www.flyinggiants.com/forums/showthread.php?t=189835#post2450065

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@Nutball,

It looks like Anthracite Coal to me. But the other possibility is Hematite.

Given that you found it near a railroad track I would guess that was Anthracite which fell off a coal car on its way from Pennsylvania to wherever it was going.

Farmerman will be able to give you some better ways to determine exactly what it is.

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@rosborne979,

Checking other pics online I think you are right about it being anthracite. I wonder what makes some pieces so shiny and silver? I just read something about the silver pieces being very black, perhaps just highly reflective. I'm surprised it didn't burn with the propane torch, I might throw it in the wood stove and see what happens.

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@rosborne979,

Maybe it is not anthracite, or just some variation that doesn't burn well. I put the piece buried in some glowing wood coals in the wood stove right in front of the air vent. The wood coal was glowing white hot, almost blue hot, the rock was a bright red as far as I could tell although still very reflective. After maybe an hour of that I pulled it out, let it cool and it is completely unchanged. After some reading it looks like anthracite can be started by wood coals. Of course it wasn't in an ideal environment surrounded by lots of anthracite coals, but to help it get going it was surrounded by some pieces of lower grade coal and wood coals.

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@Nutball,

Well then, the only other thing I can think of is Hematite. You might be able to google a test for that, but I don't know of one off-hand.

I left a message for Farmerman to have a look at this thread. He is a professional geologist so I'm sure he can help. But he may be off-line for a while.

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@rosborne979,

Thanks, I added a pic of a smaller piece of hematite next to the non magnetic silver rock which is still 17g after being in the stove.

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@Nutball,

Hematite will leave q red streak on a piece of unglazed tile, and is fairly magnetic. Just because the rock didnt burn outright it could be highly metamorphosed and the carbon is in a denser crystal. Having said that I dont reccommend EVER doing destructive tests if you want to keep something. Coal can be best tested by taking a red hot needle (HOLD IT WITH LONGNOSE PLIERS) and touch the sample somewhere that wont be seen. You can smell the coal-like odor (sulfurous and burning smell)

Did you do any tests that didnt include burning it ?( like a streak plate or holding near a magnet?)

There i a very dense form of anthracite with higher metamorphosed carbon like streaks of graphite.

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@farmerman,

Comparing it to hematite, exposing both to a magnet, the hematite was slightly magnetic and the silver rock not magnetic, hematite seems denser too. The streak is a reflective silver. Assuming it was anthracite, I find it more interesting in burning it and confirming what it is than keeping it.. I may have gotten the density number in the first post slightly wrong if that means anything. It seems highly conductive, cold to touch and quick to transfer heat from one end to another. It smells like some sort of hot metal when heated, not carbon steel, it almost has kind of a sweet metallic smell if you know what I mean, but that may have been picked up from the fire place. The smell seems to be a variation of the way the metal case of little dc motors smell. No sulfurous or burnt heavy oil smell when heated.

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@Nutball,

I'd consider it being zinc, but it is too light weight.

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@farmerman,

I think it can scratch glass and hematite, but as rough as the surface is, I'm not surprised if it could make small scratches on something harder than itself. I did another streak test, but on a black surface comparing stainless steel, hematite, the rock, and pencil graphite. The picture is now with the others. The rock streak is a slightly darker grey than stainless steel, and looks like it is from a harder material as it doesn't lay down it's substance on the plate as readily as the other minerals.

Also it has much lower electrical resistance compared to hematite, but it was also much harder to get a good connection resulting in a measurable low resistance compared to hematite. I'd touch the probes to it and often got no reading, but when I would get a very firm connection it would be around 50 ohms across the whole rock, the hematite readily showed a few kohms to 2Mohms at the slightest contact.

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