New Mineral Named After GIA’s John Koivula
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 Post subject: Green Tourmaline... no chrome in it, but really bright
PostPosted: Thu Jul 13, 2017 11:21 am 
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Dear friends,
I have bought this green tourmaline from Namibia
its about 1 carat, well cut in stepped octagon.
The color is intense green, with a hint of yellow. It does not turn red under Chelsea filter, thus no chrome is in this stone.
I wonder whether such a bright green is due to iron. I know, in fact, that green tourmalines are often colored by iron, but this one is particularly vivid.
here some pics
Image
Image
Image
Image

Thank you for all the replies
:D :D :D


Last edited by Luca on Fri Jul 14, 2017 3:09 am, edited 1 time in total.

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 Post subject: Re: Green Tourmaline... no chrome in it, but really brigh
PostPosted: Thu Jul 13, 2017 12:43 pm 
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Tourmaline can have so many variables when it comes to the transition metal impurities which cause color.
Fabulous color!

http://www.elementsmagazine.org/archive ... zzotta.pdf


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 Post subject: Re: Green Tourmaline... no chrome in it, but really brigh
PostPosted: Thu Jul 13, 2017 1:40 pm 
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Like it very much! Great color...

Found this bright 2,20 ct in St Marie aux Mines.

Sold as a "Merelani" Diopside - the dichroism was to strong and I liked it very much so I took it. With a little hope that it could be a bright green kornerupine too. At the moment they offer some.

So "only" tourmaline - orign unknown - maybe Mozambique ( dealer is specialized in Tanzania gems ) or another african source.

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Eyeclean with very nice cutting.

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 Post subject: Re: Green Tourmaline... no chrome in it, but really brigh
PostPosted: Thu Jul 13, 2017 3:12 pm 
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The stone in the original post looks nice but also typical of tourmaline? Maybe it's just my monitor but I don't see anything that makes me think it wouldn't be iron colored, it's just a nice example.

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 Post subject: Re: Green Tourmaline... no chrome in it, but really bright
PostPosted: Fri Jul 14, 2017 3:29 am 
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@Barbra thank you for the suggested reading :D
It is really interesting!!!

@Marlow I really like your tourmaline with this nice mint color... :D I think this particolar hue is rare in a tourmaline.

@Stephen Maybe my tourmaline is colored by iron. However, it seems to me different from other tourmalines I have seen before. So, I supposed that this bright green might be due to a different element.
I have read that some green tourmalines (with no red reaction at the Chelsea filter) are colored by vanadium.


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 Post subject: Re: Green Tourmaline... no chrome in it, but really bright
PostPosted: Fri Jul 14, 2017 2:18 pm 
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Small stones and the bigger one is included but nice color. Nigerian origin. 0.75ct. and 1.19 cts.


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 Post subject: Re: Green Tourmaline... no chrome in it, but really bright
PostPosted: Sat Jul 15, 2017 5:11 am 
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@Seaglow
Very nice stones! :D


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 Post subject: Re: Green Tourmaline... no chrome in it, but really bright
PostPosted: Sat Jul 15, 2017 6:59 am 
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Luca, no red fluorescence, so most likely vanadium.


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 Post subject: Re: Green Tourmaline... no chrome in it, but really bright
PostPosted: Tue Jul 18, 2017 4:37 am 
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Attachment:
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Ive posted this pic before because this is chrome tourmaline, african origin & is not readily easy to come by even on the webs, it will change to a reddish color under a chelsea filter & will also change under incandescent light, the chrome content is so high in these stones- 8)


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 Post subject: Re: Green Tourmaline... no chrome in it, but really bright
PostPosted: Tue Jul 18, 2017 2:07 pm 
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Everyone who has followed my posts over time knows that simply being colored by a specific elemental chromophore does not guarantee beauty.

Modifiers like copper, chromium, are often used as hype to promote gems which would be hard to sell otherwise.


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 Post subject: Re: Green Tourmaline... no chrome in it, but really bright
PostPosted: Tue Jul 18, 2017 2:53 pm 
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If i may please add-maybe not beautiful, but unique for what they are, nature adds true gems to the menu & variety to see-Ive seen some unique gems in the last few months that were not seen before or were not known of, so to speak- :?: 8)


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 Post subject: Re: Green Tourmaline... no chrome in it, but really bright
PostPosted: Tue Jul 18, 2017 4:16 pm 
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Well, sometime they are not "beautiful" but really interesting....

2,58 ct UE Tourmaline...

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LED - quite close to daylight color which is a bit better and cooler green.

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Incandescent light - both pics

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 Post subject: Re: Green Tourmaline... no chrome in it, but really bright
PostPosted: Tue Jul 18, 2017 4:52 pm 
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I have one of those large UE chrome tourmalines as well. It's one of my favorite stones, I admit, but from an aesthetic point of view is so dark that under "normal" illumination is almost black.

Only with strong illumination I get bright green and red sparkle. :) Really beautiful, but if I were to choose a stone to wear, that's just too dark. I'm always tempted to recut it, but I'm sure it won't improve it much, if at all, so I have to live with it...


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 Post subject: Re: Green Tourmaline... no chrome in it, but really bright
PostPosted: Tue Jul 18, 2017 11:36 pm 
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Fortunately my stones is not to dark and custom cut ( Coast to Coast ).

A friend of mine, Uli Zeisberg, bought nice CC garnet rough with a visible usambara effect - first time I could see it in garnet. Greyish green bodycolor in daylight but the thicker part in the middle was greyish pink. Can't wait to see the cut stone.

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 Post subject: Re: Green Tourmaline... no chrome in it, but really bright
PostPosted: Sun Jul 23, 2017 9:55 am 
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Thank you all for the replies,
I definitely agree with Barbra that one specific chromophore (Cr, Vn, Cu) doesn't necessarily confer beauty to a stone.
However, it seems to me that the trade market does take this aspect in great consideration.
In particular, in my old edition (2015) of the Gem Guide, green tourmaline under 1 ct is valued 25-40 dollars for the fine quality and 40-60 dollars for the extrafine quality.
BTW, I have paid my tourmaline more than 60 dollars per carat (no matter since I liked the color).
On the other side, in the Guide chrome tourmaline is valued much more (125-250 dollars per carat for the extrafine quality).
Thus, it seems that the presence or the absence of a specific chromophore is more important than beauty to estimate the value of a gem?
Why?
thank you
:D :D :D :D


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