Novembr 16-18—COLUMBIA, SOUTH CAROLINA: Annual show; The Columbia, SC Gem and Mineral Society; Fri. 10-6, Sat. 10-6, Sun. 12-5
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 Post subject: Re: Single Source Gems May No Longer Be Single Source
PostPosted: Thu May 10, 2018 12:16 am 
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Yes in ebay you find many sellers who claim to sell afghan tsavorites. At least claim ;)
As Barbra asked for reference I did not wanted to use ebay as many people do not see ebay as a serious platform to buy rough/cut stones from. I made plenty of good experiences there but this can be a personal and lucky experience.

I bought my canadian tsavorites on canadian fairs from canadian sellers, but the green grossulars are there. The color fits for tsavorites for some of these stones (yes its possible to discuss which one in detail is tsavorite or "only" grossular). But as shown with some links they are there.
Also very fascinating are the greendot grossulars from jeffrey mine.

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 Post subject: Re: Single Source Gems May No Longer Be Single Source
PostPosted: Fri May 11, 2018 5:13 pm 
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The color is correct for the Canadian tsavos but the chemistry is not. :D
See:
viewtopic.php?f=6&t=24455&p=240350#p240350

Perhaps it is a similar situation with pezzottaite. Just throwing that out there. I have nothing to back that up.
Perhaps Chris Smith does (hint hint)


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 Post subject: Re: Single Source Gems May No Longer Be Single Source
PostPosted: Fri May 11, 2018 5:27 pm 
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The chemistry is different on the canadian grossulars for sure, but I don't think that should matter. We made that mistake with emeralds and have largely lived to regret it.
Pezzottaite is a bit less i tricate than the garnet group. Just a big handful of cesium for mineral identity and a pinch of manganese for color.


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 Post subject: Re: Single Source Gems May No Longer Be Single Source
PostPosted: Fri May 11, 2018 5:40 pm 
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:smt017 Two sides to that pancake.


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 Post subject: Re: Single Source Gems May No Longer Be Single Source
PostPosted: Fri May 11, 2018 5:56 pm 
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Stephen Challener wrote:
The chemistry is different on the canadian grossulars for sure, but I don't think that should matter. We made that mistake with emeralds and have largely lived to regret it.


Once again the peculiarities of the gem business shows itself to be illogical. The African Emerald is said to lessor because it is colored by Vanadium, not Chromium. The Canadian garnet is said to be not as good because it is colored by Chromium and lacking in Vanadium. In my opinion, what should matter is the beauty of each stone, but that is not how this cookie crumbles. :roll:


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 Post subject: Re: Single Source Gems May No Longer Be Single Source
PostPosted: Fri May 11, 2018 9:00 pm 
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If I remember correctly, both the emeralds from the Kafubu Area in Zambia and the Sandawana emeralds in Zimbabwe can have a high Fe content. I think the Fe is more of a sting than the V. Iron tends to "ink" gems up, IMO.

I was able to find an old post by Rick Martin 2006...
ROM wrote:
1. Fairly dark-toned green beryl with iron as the chromophore exists and has been represented by some sellers as emerald. I've seen images of such material but can't recall exactly where. There are some authorities who claim that beryl with any chromophore other than chromium is not truly emerald. That would include beryls from Zambia and some areas in Brazil and elsewhere that have a vanadium chromophore, as well as the iron-colored beryl.

2. The issue of how to distinguish between "green beryl" and "emerald" came up some time back on another forum and I repeated what I'd been taught about chromium being the basis. I was informed that GIA now uses color only, not chemistry, to make the distinction. (My GIA lessons are old and I can't find that distinction). I was curious how the AGTA viewed the issue and wrote Richard Hughes to ask. (He'd recently taken the post of lab director for AGTA).*

I received a response from him dated 1-4-06. My question to him was this:

"Does the AGTA Lab* have a position on what chromophore is necessary to make emerald out of green beryl? Or what differentiates emerald from green beryl?

"I've always been told emerald must contain chromium. But I see that vanadium-as-chromophore has apparently been accepted in the marketplace for Zambian and Brazilian goods. What about iron?

"Would the presence of vanadium or iron affect the quality determination of an AGTA emerald cert? That is, would the stone be downgraded in any respect?"

His answer:

"Thanks for your note. Emerald is a variety defined by color rather than coloring agent. Thus if a stone has a color similar to a normal emerald, it would get the emerald variety name. Hope that clears it up for you ;-)"

So there you have it. I'm not an advocate for either position. I'm merely reporting the facts as I interpret them.

Rick Martin


*the AGTA Lab is no longer operational


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 Post subject: Re: Single Source Gems May No Longer Be Single Source
PostPosted: Fri May 11, 2018 9:30 pm 
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Gemologically I think the industry has largely settled this issue. Emerald is a beryl with a particular range of primary color, tone, and saturation. The exact boundary varies slightly in different parts of the World. However, premiums in price are still affected by tradition, provenance, origin and chromophore.


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 Post subject: Re: Single Source Gems May No Longer Be Single Source
PostPosted: Fri May 11, 2018 10:04 pm 
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Totally agree.


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 Post subject: Re: Single Source Gems May No Longer Be Single Source
PostPosted: Sat May 12, 2018 12:09 am 
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Chromium and vanadium are geochemically similar so they're usually both present. It's certainly not impossible to find them in isolation, but if I remember right those 'vanadium emeralds' from Africa ended up having significant chromium content all along. Certainly the Zambian and Nigerian ones do anyway. I have had the 'vandium beryl' look described to me as a more blueish green color, but synthetic vanadium-only beryls actually show a slightly yellowish green color, so presumably it is indeed the higher iron content that gives them a different look:
Image
"Figure 9: The slightly bluish green coloration of the new type of Tairus synthetic emerald (top, 7.52 ct, 16.5 × 7.5 mm) is caused by superimposition of the light blue colouration of a synthetic copper-bearing beryl (below left) and the yellowish-green colouration of a synthetic vanadium-bearing beryl (below right); the copper- and vanadium-doped samples are Russian research samples obtained by one of the authors in the early 1990s. Photo by M. Glas."

As a side-note, this is what I think of when I hear 'saturated green beryl colored by iron':
Image
(picture from Spirifer Minerals)
I mean, that's impressive depth of color for a green fe-colored beryl, but who would ever mistake it for emerald? I suspect heliodor yellow and aquamarine blue just aren't quite compatible enough to get a rich green color when mixed. I'll admit I've seen a few lighter toned unheated green aquamarines that in the right light (specifically fluorescent) might be mistaken for a very blueish emerald though.


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 Post subject: Re: Single Source Gems May No Longer Be Single Source
PostPosted: Sat May 12, 2018 1:26 am 
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I can tell what I'm doing tomorrow.....dividing this thread into several other threads. :oops:

When I was almost young, I remember the first African emeralds which hit the market. They were mined in Zambia and always cut in Israel.
There was a profound bluish component:
Image

When I spoke of Fe as a significant chromophore,it was in concert with other elements...not solo.

GIA wrote:
The most important chromophore in Zambian emeralds is Cr, which averaged 0.26 wt.%—and ranged up to 0.84 wt.%—Cr2O3. Overall, the darkest green stones had significantly higher Cr contents than the lighter and medium green stones, which often showed no straight forward correlation between color intensity and average Cr content. In contrast, V concentrations were consistently low, averaging just 0.02 wt.% V2O3 and attaining a maximum of 0.09 wt.% V2O3.
The only other significant chromophoric element was Fe, which averaged 0.76 wt.% oxide (as FeO)and showed a maximum of 1.75 wt.% FeO.


Fe typically (in my experience) dampens vividness.

Please feel free to disagree with me.

And Steve, I'm sure you saw some of the first African emeralds distributed by Israeli dealers. Have any recollections?


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 Post subject: Re: Single Source Gems May No Longer Be Single Source
PostPosted: Sat May 12, 2018 2:34 am 
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Barbra Voltaire wrote:
When I spoke of Fe as a significant chromophore,it was in concert with other elements...not solo.

Oh yeah, absolutely. I meant it in reference to ROM's post.


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 Post subject: Re: Single Source Gems May No Longer Be Single Source
PostPosted: Sat May 12, 2018 10:24 am 
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Yes, I remember seeing the stones that started coming out of the Israeli/ Zambian connection, knew many of the rough buyers in Africa. I always accepted Zambian stones as Emerald, but thought most were too blue to stand up to Colombian in desirability. The one thing that the Israelis did bring to the market was a much larger assortment of shapes, matching, and calibration. This was a great thing for the market in my opinion.

Rarely I would see in the market the Lake Manyara stones. The finest of which I thought rivaled traditional sources. I also remember the small calibrated stones coming out of Sandawana. The finest stones from here were dark, holding color in even the smallest cut stones. However, stones from these sources were never available to me in a quantity to be commercially viable.


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 Post subject: Re: Single Source Gems May No Longer Be Single Source
PostPosted: Sat May 12, 2018 1:55 pm 
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Barbra Voltaire wrote:
If I remember correctly, both the emeralds from the Kafubu Area in Zambia and the Sandawana emeralds in Zimbabwe can have a high Fe content. I think the Fe is more of a sting than the V. Iron tends to "ink" gems up, IMO.

On an atom-by-atom basis (not a wt.% basis), Kafubu Zambia emeralds have as many Fe atoms as Cr atoms, and usually more. Those emeralds have essentially no V atoms at all. I don't know where this misinformation that African emeralds have significant V content comes from, but it is wrong. The blue in bluish green African emeralds comes from the Fe and the dominant green comes from the Cr, even though in many cases there are actually fewer Cr atoms.

To address another point of misunderstanding. Colombian emeralds typically have roughly the same atom-by-atom concentrations of V and Cr. One individual sample may have more Cr than V and another may have more V than Cr. But no Colombian emerald I've come across has ever had a negligible amount of Cr.


Last edited by Brian on Sat May 12, 2018 8:34 pm, edited 2 times in total.

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 Post subject: Re: Single Source Gems May No Longer Be Single Source
PostPosted: Sat May 12, 2018 2:17 pm 
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I've changed the name of this thread to be a bit more encompassing:
Re: Single Source Gems May No Longer Be Single Source

:smt023 I'll drop Chris Smith a note and get his take on Single Source Gems.


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 Post subject: Re: Single Source Gems May No Longer Be Single Source
PostPosted: Sun May 13, 2018 6:03 am 
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Interesting....

You discuss "Emerald" - a variety of Beryl and "Tsavorite" a variety of Grossular...

What about "Demantoid"??

Is Demantoid the yellowgreen to fine vivid green to deep green variety of Andradite coloured by chromium?

Or only a fine green variety of Andradite like some of the russian stone ( and this source produces brown, yellow and yellowgreen stones too) and some of the iranian stones and very rare items from Canada should be labeled as Demantoid?

Have your ever seen a very fine one from Madagascar, Namibia or Italy or Mexico in the color of the best russians stones.

Is chromium always responsible for the color of Demantoids from MAD, NAM, I or MEX or the lower russian qualities?

Nobody would neither call the green beryl crystals posted here as emeralds nor the yellowgreen grossular as tsavorites..

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