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 Post subject: Could This Be A Rough Carbonado Black Diamond ?
PostPosted: Sun Jan 27, 2013 2:05 pm 
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Hi I would be very grateful if a Gemologist who has experience with rough black diamonds could have a look at a very interesting object I have. This object is not like anything from my area of the UK. After doing some research of my own the closest thing this object looks like is a Carbonado diamond. A brief description about the object is that it has a high refraction, looks polycrystalline in structure with tiny holes over it. It has a greasy, porous texture. It is slightly magnetic and is very hard. Anyway I will link to the video on youtube as this is the best way to show its refraction, texture etc as you can pause at any time to get a closer look. I look forward to a professional opinion and would be grateful if anyone could tell me where I could get it tested or look at within the UK. Thanks again



Or copy and paste this: http://www.youtube.com/watch?v=foNgE63n0uc for full screen.


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 Post subject: Re: Could This Be A Rough Carbonado Black Diamond ?
PostPosted: Sun Jan 27, 2013 3:40 pm 
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I do not think it is diamond. Carbonado is polycrystalline, but from what I have read and the pictures I've seen, the crystals are very small and sintered together, not large like these. This leads to a smooth surface. To me, the flashing crystal/cleavage faces on your stone make me think it contains feldspar, and my guess would be that it is a chunk of gabbro--I have seen some with a very similar overall appearance, especially the surface texture with the feldspar crystals. But that is just a guess.

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Last edited by Stephen Challener on Sun Jan 27, 2013 11:57 pm, edited 1 time in total.

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 Post subject: Re: Could This Be A Rough Carbonado Black Diamond ?
PostPosted: Sun Jan 27, 2013 6:30 pm 
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Would a thermal diamond tester work on carbonado?


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 Post subject: Re: Could This Be A Rough Carbonado Black Diamond ?
PostPosted: Mon Jan 28, 2013 1:18 pm 
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Thanks for reply but not all Carbonados have a glassy appearence as you can tell from this small piece of Carbonado from Brazil that clearly shows the iron inclusions
http://www.flickr.com/photos/14833125@N02/4355006353/

But I would agree that the specimen I've shown does have a larger range of small crystals, ranging from nano size to larger but I think this might be because of a melted surface which has then re-crystallized. Also Gabbro is not native to my area at all. I have no Idea if a thermal diamond tester would work on a carbonado but any information is welcomed and appreciated. And if I was compelled to get it tested (chemically or otherwise) where would I go within the UK.


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 Post subject: Re: Could This Be A Rough Carbonado Black Diamond ?
PostPosted: Mon Jan 28, 2013 2:41 pm 
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Wikipedia wrote:
re:
Extraterrestrial origin hypothesis of Carbonado
Supporters of an extraterrestrial origin of carbonados, such as Dr. Stephen Haggerty, a geoscientist from Florida International University, propose that their material source was a supernova which occurred at least 3.8 billion years ago. After coalescing and drifting through outer space for about one and a half billion years, a large mass fell to earth as a meteor approximately 2.3 billion years ago, possibly fragmenting during entry into the Earth's atmosphere, and impacting in a region which would much later split into Brazil and the Central African Republic, the only two known locations of carbonado deposits.
Mystery Diamonds. Geoscientists Investigate Rare Carbon Formation, American Institute of Physics, June 1, 2007; associated video

Getting back to your question, I suspect a diamond tester would work on carbonado. Why don't you try it and report back.

Or, bring it to the earth sciences department in the closest college or university and ask a petrologist to help you identify your unknown.


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 Post subject: Re: Could This Be A Rough Carbonado Black Diamond ?
PostPosted: Mon Jan 28, 2013 3:53 pm 
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Air wrote:
Thanks for reply but not all Carbonados have a glassy appearence as you can tell from this small piece of Carbonado from Brazil that clearly shows the iron inclusions
http://www.flickr.com/photos/14833125@N02/4355006353/

But I would agree that the specimen I've shown does have a larger range of small crystals, ranging from nano size to larger but I think this might be because of a melted surface which has then re-crystallized.

Little phenocrysts, sure--but those are honking big crystals on your rock. Melting and recrystallization doesn't produce large crystals over short time periods--crystals take time (usually quite a bit of time) to grow large.
Air wrote:
Also Gabbro is not native to my area at all.

Nor is carbonado. I'd like to be wrong, but your rock looks pretty igneous to me.

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 Post subject: Re: Could This Be A Rough Carbonado Black Diamond ?
PostPosted: Mon Jan 28, 2013 4:06 pm 
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Barbra Voltaire wrote:
Would a thermal diamond tester work on carbonado?

Yes it would.

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 Post subject: Re: Could This Be A Rough Carbonado Black Diamond ?
PostPosted: Mon Jan 28, 2013 4:08 pm 
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The Carbonados I have experience with are spheroidal in shape and lap very slowly in certain directions. The facet surfaces do not polish to the quality of single crystal diamond.
I don't think the piece the OP displayed is Carbonado.

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 Post subject: Re: Could This Be A Rough Carbonado Black Diamond ?
PostPosted: Mon Jan 28, 2013 4:37 pm 
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I agree with thomas.adamas and Scarodactyl.
I don't think this specimen in carbonado.....but now we know, a thermal diamond tester will definitively solve the controversy.

Let us know what you discover Air.


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 Post subject: Re: Could This Be A Rough Carbonado Black Diamond ?
PostPosted: Tue Jan 29, 2013 2:28 pm 
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Why not determine it's SG?


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 Post subject: Re: Could This Be A Rough Carbonado Black Diamond ?
PostPosted: Sun Mar 03, 2013 8:55 pm 
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I'd suggest taking it to a local gem & mineral club, or geology/mineralogy dep't of a local museum or university, if we can't convince you that it's a chunk of feldspar or somesuch instead of the biggest diamond ever found in Britain.

I find common sense is always of help in this type of situation.

When you hear hoofbeats in Britain, what animal do you expect to be coming around the corner... a horse, or a zebra?

Thinking diamond is like thinking zebra.


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