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 Post subject: Identifying Faceted Black Gems
PostPosted: Tue Oct 14, 2014 12:12 pm 
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I've created a new area on our forum for Stone Group Labs!
Bear and Cara Williams have studied, experimented and documented many topics which are very useful for all.

If you had overlooked this article from last year, give it a read now:
Click here for direct link.
[pdfview]http://stonegrouplabs.com/wp/wp-content/uploads/2013/01/TheBlackGemChallenge.pdf[/pdfview]

I have a follow-up question,
Couldn't black Spinel also be identified with a Raman?


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 Post subject: Re: Identifying Faceted Black Gems
PostPosted: Tue Oct 14, 2014 1:34 pm 
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Cool article.

I recently had someone send me a supposed black spinel for use as an accent stone with her Maw Sit Sit jade. Upon looking closer, it had that typical too-dark rhodo/pyro garnet color in strong transmitted light. I told the client my suspicions, but in this case it wasn't a big deal.

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 Post subject: Re: Identifying Faceted Black Gems
PostPosted: Tue Oct 14, 2014 1:50 pm 
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Hi Eric,
From your description, I would think you might be able to get an RI reading. Black spinels are quite different that their translucent brethren, which usually have an RI close to 1.72. Almandine garnet can also be OTL.


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 Post subject: Re: Identifying Faceted Black Gems
PostPosted: Tue Oct 14, 2014 1:56 pm 
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Hi Barbra,

To be honest, I have only tried the black spinels with our old Enwave Raman with the red (789nm) laser, which would give a flood reaction. Since then we have the new Gemoraman SG with the green (532nm) laser and I may well get better readings with that. Let me pull some lab samples, run the tests, and get back to you with the results. Alberto, Mikko,...have you played around with testing black spinels?

Cara


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 Post subject: Re: Identifying Faceted Black Gems
PostPosted: Tue Oct 14, 2014 2:23 pm 
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Barbra, I thought that we did get some readings on Raman with black spinel, but now reading Cara's message... I can't remember. Hey, that might make a nice password. When I don't get results on Raman, I will often run a reflectance FTIR and those give up the answers very well.

Glad to be back on GemologyOnline :o


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 Post subject: Re: Identifying Faceted Black Gems
PostPosted: Wed Oct 15, 2014 5:46 am 
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black materials are not good Raman scatterers in general, and commonly tend to absorb a lot of radiation without emitting a decent amount back. Tomorrow i will receive some new samples and run some scans over'em. Hope to be able to report results soon.. :wink:


Bear Williams- SGL wrote:

Glad to be back on GemologyOnline :o


glad to see u here again!! :D :D :D

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 Post subject: Re: Identifying Faceted Black Gems
PostPosted: Thu Oct 30, 2014 12:03 pm 
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Sorry for the delay in responding, but Alberto is correct. Black spinels defy almost all standard testing and some advanced testing equipment as well. Raman does not give readings on them, but it should identify the alternatives. If you don't need 100% confirmation (they are so inexpensive you usually would not), you can try for an RI. If you get one (and you are not reading your RI fluid) then you have probably ID'd what it is and it is not black spinel. If it is very high lustre it is probably not black spinel but CZ or moissanite or diamond. If it is low lustre it could be schorl (black tourmaline). Black spinel has a vitreous lustre and is smooth, with few surface irregularities.

They can be dragged with a rare earth magnet, but many black minerals will also.


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 Post subject: Re: Identifying Faceted Black Gems
PostPosted: Thu Nov 20, 2014 11:40 pm 
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Just got in a batch of a dozen "black diamonds", some with accompanying reports (from the GLI) determining that they were authentic black diamond. It's nice to see how well the GemmoRaman performed to quickly determine they were all synthetic black Moissanites.

There was also a decent reaction to the Nd magnet where the black moissanite could almost be pulled across the desk.


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 Post subject: Re: Identifying Faceted Black Gems
PostPosted: Fri Nov 21, 2014 12:59 am 
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Just an addendum - black moissanites are not the only black gems that have a strong magnetic pull. Black spinel does, as do some carbonado diamonds.
And as an alert, I would say that a significant percent of the black moissanites we see are accompanied by lab reports stating that they are diamond. While I've no idea if it is intentional fraud, I do know that labs that are not aware of these and do not have the right equipment are very likely to make this mistake. There have been a number of these sold in auctions, again with incorrect lab reports.


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 Post subject: Re: Identifying Faceted Black Gems
PostPosted: Fri Nov 21, 2014 8:07 am 
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I've not purchased any myself as of yet, but I always assume all solid black stones that are labelled diamond are probably synthetic moissanite. I know black diamonds exist, but I'm not convinced I've ever seen a real one.


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 Post subject: Re: Identifying Faceted Black Gems
PostPosted: Fri Nov 21, 2014 3:12 pm 
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Please pardon me, but I can't resist from pointing out the following references:
Gems and Gemology, summer 1977, and Lapidary Journal, June 1977.

Had the gemological teachers of that time been astute and not provincal, they would have taught this concept instead of their "cop-out" of OTL. Diamond and Silicon Carbide have never been a problem for white or black gems.


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