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 Post subject: natural untreated black diamond: electrically conductive?
PostPosted: Sun Feb 06, 2011 11:10 am 
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Diamonds are insulators, excepting IIb.

But what about natural untreated black diamonds?

First, what are the possible causes for the black colour:
-natural irradiation?
-graphite inclusions?
-black metal oxides/sulfides?
-opaque polycristalline structure?
-very dark gray, brown, green or blue color?
-other?

So, in your experience, do some natural untreated black diamonds conduct electricity?

and would some of these be detected as moissanite by a diamond-moissanite tester that relies on the electrical conductivity to discriminate moissanite?


Last edited by cascaillou on Thu Jan 12, 2012 3:27 pm, edited 1 time in total.

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 Post subject: Re: natural untreated black diamond: electrically conductive
PostPosted: Sun Feb 06, 2011 12:12 pm 
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My Presidium duotester has no problem at all to identify a black diamond as a diamond, neither there is any problem to identify moissanite with it... I have not had any black moissanite yet to test...

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 Post subject: Re: natural untreated black diamond: electrically conductive
PostPosted: Sun Feb 06, 2011 1:45 pm 
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There has been a tremendous amount of misinformation published concerning black diamonds in the past.
It was not until Eric Bruton, published his book, Legendary Gems or Gems that Made History in 1986 that some clarity was shed on natural black diamonds.

Quoting from that book, pp110-111:
Eric Bruton wrote:
Prominent diamontaires have long declared that there are no black diamonds-that they exist only in detective stories. The origin of this belief may be that some so-called black diamonds are actually dark brown with so many specks of dark mineral inclusions that they only appear black.
Image


Natural "black" diamonds when viewed with magnification will have some transparent areas. The black appearance is caused by numerous black inclusions that line an extensive network of internal cleavages and fractures.

The polish on these heavily included "black" diamonds is usually rather poor, exhibiting pitted facet junctions, and polishing and drag lines are usually visible on the facets. Diamond cutters often complain that black diamonds are VERY hard to polish and can often damage a polishing lap.
Image

It has also been noted that a 595nm absorption line can be found in natural black diamonds and will not be seen in artificially irradiated diamonds.

All black diamonds which have been reported in gemological literature have been thermally conductive, therefore clearly resulting in "DIAMOND" readings on thermal diamond testers.

Artificially irradiated "black" diamonds are actually a very dark green color, not really black at all. Artificially irradiated "black" diamonds can be easily separated from natural "blacks" by observing them with transmitted light through a thin portion of the gem (like the girdle or culet). The color will appear a very dark green.

Artificially irradiated diamonds will also test as "DIAMOND" with a thermal tester.


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 Post subject: Re: natural untreated black diamond: electrically conductive
PostPosted: Sun Feb 06, 2011 4:35 pm 
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you can identify natural black diamonds from irritated black diamonds with standard gemological microscope. the color of natural black and very dark gray is cause by black inclusions like graphite, hematite, magnetite and native iron.
natural black diamonds are often highly fractured and shows pits and polishing and drag lines.
the cleavages you see in natural black diamonds are often lined with graphite , with natural black colored diamonds using transmitting light you will see black inclusions through the stone, natural black diamonds show randomly dispersed throughout the stone, black inclusion called a salt and pepper appearance

when Irradiated black diamonds viewed with strong transmitted light the true body color are usually prove to be very dark green, this color maybe absorbed in very large areas of the diamond. a very dark blue body color may also result from transmitted light both of these body color will appear black in reflected light.

although Irradiated black diamonds usually appear very dark green in transmitted light some stones that are irradiated to a very dark green color are subsequently annealed to a very dark orange color,
these body colors only are noticeable in thin areas around the edge of the stone viewed with strong transmitted light.

another treatment process that can create black color in diamonds is heating in a vacuum, the starting material is a milky white highly fractured diamond
after heating in a vacuum the diamond will appear black due to graphitization of surface reaching fractures, diamond treated by this process will show graphitization that is confined to the surface areas of surface reaching fractures

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 Post subject: Re: natural untreated black diamond: electrically conductive
PostPosted: Sun Feb 06, 2011 6:46 pm 
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thanks for all the good info, you're quite helpful here.

one last thing: do some natural untreated black diamonds conduct electricity?

From the link I posted in my previous thread, it is said that black diamonds have been imitated by coating poor quality diamonds with DLC, and it says that
Quote:
DLC is strongly electrically conductive, any black diamond with such conductivity is suspicious

Does that mean that some black diamonds also conduct electricity but not as much as DLC?
If so, I guess that would be due to inclusions (graphite), right?


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 Post subject: Re: natural untreated black diamond: electrically conductive
PostPosted: Wed Feb 09, 2011 9:47 pm 
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anyone?


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 Post subject: Re: natural untreated black diamond: electrically conductive
PostPosted: Wed Feb 09, 2011 11:04 pm 
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cascaillou wrote:
Does that mean that some black diamonds also conduct electricity but not as much as DLC?
If so, I guess that would be due to inclusions (graphite), right?

Eric Bruton, in "Diamonds," states that "As there are no free electrons or holes in a perfect diamond crystal lattice, diamond has high resistance to the passage of electricity. Graphite, owing to the loose bonding between scales, has free electrons which provide the ability to pass an electric current."

However, in a study of Yakutian black diamonds mainly from the Mir diamond pipe in Siberia (Gems & Gemology, Fall, 2003) researchers concluded that extremely tiny amounts of graphite -- long suspected to be the cause of black diamonds' color -- were found in only a couple of their samples. Electron microscopy showed the coloring of black and dark gray Siberian diamonds was due mainly to inclusions of magnetite, hematite and native iron, which made them magnetic to varying degrees.

They suggested the unusual magnetic properties of natural-color black diamonds might be useful in separating them from irradiated black stones and those that are heated in vacuum to cause internal graphitization.

From that I'm taking a WAG that electrically conductive black diamonds are probably more likely to be treated (graphitized) than natural.

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 Post subject: Re: natural untreated black diamond: electrically conductive
PostPosted: Mon Feb 21, 2011 7:29 pm 
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I finally found an answer in a reputable book about diamonds: natural black diamonds can indeed be electrically conductive due to the graphite inclusions.


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 Post subject: Re: natural untreated black diamond: electrically conductive
PostPosted: Thu Jan 12, 2012 1:11 pm 
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hi

i had the chance to run some fast tests on black diamonds melee in the 0.10-0.20 sizes.
they were completely black, no chance to get a single photon of light from a 150 W fiber bundle. surface was disseminated of tiny pits, polishing was good, magnetic behaviour.
submitted later to IGI antwerp, turned out to be natural black diamonds, quoting the report: "the majority of the submitted tested diamonds presents signs of enhancement by graphitization"

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 Post subject: Re: natural untreated black diamond: electrically conductive
PostPosted: Thu Jan 12, 2012 3:24 pm 
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yep, and graphite either as a natural inclusion or from artificial graphitisation provides electrical conductivity in many black diamonds


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 Post subject: Re: natural untreated black diamond: electrically conductive
PostPosted: Thu Jan 12, 2012 11:41 pm 
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Seems like Alberto said the natural black diamonds were magnetic.
Could that separate natural from synthetic black diamonds?


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 Post subject: Re: natural untreated black diamond: electrically conductive
PostPosted: Fri Jan 13, 2012 9:06 am 
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I would tend to say no because as I understand it natural untreated black diamond are not necessarly magnetic, moreover synthetic diamond can be magnetic.
Concerning the artificial graphitisation of low quality natural diamonds, the process only creates graphite whih is not magnetic, but still there's a possibility that the diamond already had some magnetic inclusions before treatment.


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 Post subject: Re: natural untreated black diamond: electrically conductive
PostPosted: Thu Feb 21, 2013 2:58 am 
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so a black diamond with lots of graphite in the fractures/clivages reaching the surface, with wide transparent "colorless" areas, showing electric conductivity (not in a consistent way...in some directions and the needle goes up and down), good polish.../

is it natural black or heated black?

thanks

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 Post subject: Re: natural untreated black diamond: electrically conductive
PostPosted: Fri Feb 22, 2013 4:45 pm 
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I love all you guys. Even when a question is posted of which I have no clue of the answer...there is always someone who has either an answer or an opinion.

I love this site...I am always learning something...thanks to you all

Frank


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 Post subject: Re: natural untreated black diamond: electrically conductive
PostPosted: Sat Feb 23, 2013 5:33 am 
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Frank wrote:
I love all you guys. Even when a question is posted of which I have no clue of the answer...there is always someone who has either an answer or an opinion.

I love this site...I am always learning something...thanks to you all

Frank


Hi

On a serious point here all the points have been serious I admit. I have never tested for magnetism in the black diamond

I do know they are very brittle and people should be careful when buying the smaller chip variety as in eternity rings etc. They are very hard to cut mostly you will find the small black chips are not real.

The Blacks are usually cut in India and you can obtain a good sized natural pretty cheaply in fact up to twenty carets is still affordable. It is the setting that really costs the money.

You will find these originate from Africa

Using a 10 x lense under a good light will usually pick up a natural.

The Presidium is also useful as long as you have a good one. Of course use an RI machine (for unset stones) or a lab which is expensive.

If your in the field these instruments are delicate to carry around. (as in the field I mean shopping around)

But always use whatever tests you have available to you, do not let it go with just one.

Happy hunting

Wildwood


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