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 Post subject: Violet/grey tourmaline
PostPosted: Wed Aug 19, 2020 11:45 am 
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Location: Durban, South Africa
I've had this strange 10ct tourmaline for a couple years now and would like to know your thoughts on it. It has slight color change from dark grey-blue to grey-violet. It's from Mozambique. The rough had a crystal face with a very thin pink rind. I don't believe it was mined in the area that usually produces cuprian tourmaline but I guess it's possible that it could be cuprian. Unfortunately it was just the one stone, otherwise I'd have tried heating a smaller one. I do think this color is quite attractive as is though. It looks very spinel-like.

I don't quite know what to call this one or what kind of price I can put on it because I haven't seen anything similar for sale. Any ideas?


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 Post subject: Re: Violet/grey tourmaline
PostPosted: Wed Aug 19, 2020 12:32 pm 
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It sure looks like stones that are Mozambique copper bearing.

Heating is not the proper way to test for copper. Too much risk of damaging the stone, and ruining the nice color that it has.

It only takes a minute to take a spectra to confirm copper.

I have one similar color piece from an unknown African source. Mine is a little more grey in color. It is not copper bearing.


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 Post subject: Re: Violet/grey tourmaline
PostPosted: Wed Aug 19, 2020 12:46 pm 
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1bwana1 wrote:
It sure looks like stones that are Mozambique copper bearing.

Heating is not the proper way to test for copper. Too much risk of damaging the stone, and ruining the nice color that it has.

It only takes a minute to take a spectra to confirm copper.

I have one similar color piece from an unknown African source. Mine is a little more grey in color. It is not copper bearing.


You need an XRF spectrometer though I assume?


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 Post subject: Re: Violet/grey tourmaline
PostPosted: Wed Aug 19, 2020 1:38 pm 
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I believe anyone trying to change the color of that stone would be stone cold crazy. Just my opinion.


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 Post subject: Re: Violet/grey tourmaline
PostPosted: Wed Aug 19, 2020 2:08 pm 
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Barbra Voltaire, FGG wrote:
I believe anyone trying to change the color of that stone would be stone cold crazy. Just my opinion.


Not going to touch it. :)


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 Post subject: Re: Violet/grey tourmaline
PostPosted: Wed Aug 19, 2020 2:15 pm 
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Quote:
I don't quite know what to call this one
I'd start with extraordinary. I would consider getting a lab report for it. I think it would make selling it easier. AGL comes to mind.

Pricing something is based on comps.
Similar color.....but yours is far better in clarity.
https://www.litnon.com/index.php?page=viewgem&id=7943

Search around and see what is out there.


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 Post subject: Re: Violet/grey tourmaline
PostPosted: Wed Aug 19, 2020 2:24 pm 
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gemgalleryafrica wrote:


You need an XRF spectrometer though I assume?



Nope just a simple UV-VIS-NIR, 300 – 1,000 nm spectrometer like this one:

https://www.cigem.ca/research-technolog ... ectrometer

It is the one GIA and I both use for determining copper in Tourmaline.

I am sure many local gemologists, and any of the named international labs will have one. Most Universities or even high schools will have one.


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 Post subject: Re: Violet/grey tourmaline
PostPosted: Wed Aug 19, 2020 2:48 pm 
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Thanks for the advice, much appreciated.


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 Post subject: Re: Violet/grey tourmaline
PostPosted: Wed Aug 19, 2020 5:06 pm 
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Steve, it's on sale right now too. Thanks for the link.
Can one test mounted jewelry items ith this gizmo or only loose gems?

My Gemmoraman and EXA test jewelry or loose. The FTIR made by MAGA is limited to loose stones.


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 Post subject: Re: Violet/grey tourmaline
PostPosted: Wed Aug 19, 2020 6:02 pm 
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Barbara,

I have successfully tested mounted stones with it. The issue becomes getting a good light source through the stone. The included light housing can limit this. It is a halogen light and you can set your light baseline. So, in many cases with larger stones that don't fit in the housing, and mounted stones, you just remove the housing and position the stone so you can use a fiber optic halogen light source. The addition of a halogen light source in addition to the standard source is also sometimes required with very dark stones.

This is a very flexible tool. It does come with a limited gem database. The search/matching algorithm I find only sometimes useful. It is not a black box solution. One should be knowledgeable to use it properly.

It does have both absorption and transmission modes which I find useful. I find the transmission mode is often better for me to see patterns against the visible prism at the bottom of the screen. It is the inverse of the absorption, and the peaks become valleys right next to the prism bar. This makes it easier to visualize the absorption lines to compare to the GIA and other reference optical spectrometers pictures.


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 Post subject: Re: Violet/grey tourmaline
PostPosted: Wed Aug 19, 2020 7:17 pm 
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Thanks for the response.
When you mention the data base being small, how small?
Also, do you use it predominately to identify trace elements like copper. or for general gem identification?

Does it work for rough as well as fashioned?


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 Post subject: Re: Violet/grey tourmaline
PostPosted: Wed Aug 19, 2020 7:59 pm 
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I use it for both rough and cut stones.

The database it ships with is somewhere around 140 stones. I have added a bunch of my own so I don't remember exactly.

I use it for Gem ID just like you would your OPI. Pretty much anywhere where the GIA manual says spectrum has significance.

natural/synthetic determination particularly Diamonds looking at the Cape Line for type I.

trace elements like Paraiba, garnet species, chrome.

treatment work including Diamond irradiation.

Jade natural, dyed and polymer treating.

It has applications in all of these areas.


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 Post subject: Re: Violet/grey tourmaline
PostPosted: Wed Aug 19, 2020 8:45 pm 
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Excellent. Thanks.


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