cant be sure of anything based of the pics alone but just based on them my gut says it likely isnt even tourmaline. It is quite possibly glass.
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Thank you 
The stone has been testet for not being glass. But it can be any stone. Once it was at an auction as a tourmaline but wasn’t sold.
The stone was in a ring that belonged to the husband of the lady with the emerald ring which I posted elsewhere in this forum.
I’m not sure what you mean by tested for not being glass if it was tested then it should be known what it is. The amount of scratching is concerning. Proper superficial testing can confirm its identity if it is indeed a gemstone. Refractive index, Specific gravity, and a good look with a 10x loupe would define it or at least narrow it down to a few possible things. Unfortunately pictures alone will only get you best guess.
The texture on the pavilion face that I can see through the table is also not a helping my confidence. I went and checked my reference material and while I am in no way certain it has the presentation (in the images) of synthetic green quartz.
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Thank you for spending time helping me.
In 2000 the ring was on auction as a tourmaline. In March this year as I handed it over for auction they believed it to be a peridot but they changed the text as they put it up for sale to be a “stone” and not a peridot.
She checked the hardness of the stone in the auction house. It must have been 6.5-7 but she didn’t tell me. I don,t know why she changed her mind regarding it being a peridot. It was not until after I picked up the ring I found out about the auction in 2000.
You are probably right that it is a syntetic “stone”.
Thanks again
the fact that the listing was changed indicates that the appraiser was unsure of their assessment. Its more honest to say a stone than to claim something to be a particular stone, that way if a gemologist identifies it in the future you purchased a stone and not a peridot, if it was not a peridot you would have recourse and the appraiser and auction would be seen to have sold something that was false.
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I agree. GRS (Gem Research Swisslab) said yesterday that the stone is a tourmalin.
Another suggestion you may like to try in addition to the good advice already received. Have you looked at the stone through different angles? Tourmaline quite frequently has a ‘closed’ c-axis that can be impenetrable to light. If the stone has be cut with the wrong orientation i.e. c-axis facing up then that could account for the darkness. If there is light passing through the a & b-axes then that would be further proof.
Also it looks much too dark to be peridot.
A proper test will sort these issues out however. Good luck
Thanks, Jamie 
I have put the tourmaline on a small plastic bag with grooves, to get more light into the stone.
On the grooves of the plastic bag you can see that these are displaced where there is the closed c-axis. There appear to be two closed lines. Then the tourmaline is cut correctly, -or?
This stone has a lot of wear and it also looks like it is completely windowed, probably because it was to thin for proper angles. Because of this, if it is recut to proper angles, it looks like you are going to lose some weight…but I can’t tell how much. The ends do appear to be cut at a high angle to keep the closed C axis from showing. I think I would send this to a professional faceter for recutting, if you are sure that it is a genuine tourmaline. Such a person could tell you about what your finished weight would be and whether the color will be decent before starting any recut. If this is actually a ~26 ct tourmaline, it is worth recutting. Recutting charges should be in the neighborhood of $200-$300. A nice green tourmaline of 10-20cts should bring $100-$200/ct, conservatively, maybe more.
Think about this… if you cut a synthetic stone you have no problem of rough. Why cut with a large window when you know that it may be a problem in tha value of the stone?
As someone told you, bring the stone and look at the girdle in the two different sides in front of your eyes.
The wide side must be green, the other must be darker than the wide. If is like this, the cut is correct and you have a good probability that the stone is a tourmaline. If you think for a recut, remember this: to cut whit correct angles you must have from the girdle under the crown to the end of the stone about 60% of the lenght of the short side. So you lose many carats…
But the stone is a dark green and for this a window is less important than in a very clear and transparent stone. And for this you can see better the color. A recut whit a good symmetry and a good luster for me is enough. You lose 3/4 carats and you have a nice stone.
Be sure of the pleochroism.
Bye!
It is a 25.935 ct. tourmaline. I asked GRS to make a certificate. It should be here in about a week. I will upload the certificate when it arrives.
Hi Luigi,
Thanks for your input. How is it possible to have a transparent green color when looking through the stone on the wide side, and not being able to see anything but darkness when looking at the stone on its shorter side? Is it optical illusion?
As the GRS has seen the stone and will send a certificate, it might be better selling the tourmaline as it is, and accepting less money if a potential buyer think the stone need a recut. In this way the tourmaline and the certificate will at least match.
Hi Sabina.
Thanks for your answer. I lost your first message were you explain that you can see the color only with a light. So, if you put the stone on a white sheet near a window (but not in sun light), you cannot see the green color. Right? If is like this, the stone don’t change color also with a recut.
The stone is very damaged on the surfaces and need necessary a recut.
I hope you can sell your stone at a good price.
Have a nice day Sabina!
Bye.
Hi Luigi,
It’s exactly as you describe. In the window, where there is no direct sunlight, the stone is just dark, but as soon as it meets the sunlight, it turns green.
Would you like to make an estimate of what kind of tourmaline it is?
Thanks again for your input
Hi Sabina.
These dark green tourmalines sometimes becomes very nice with a good cut. This stone is natural and, becouse of its color, no heated. You have a certificate that confirm this. If you wont sell the stone the only buyer should be someone who can recut it. But, probably, he will tell you that the stone need time for the recut; he will lose weight and the finished stone will become smaller; becouse of the dark color is not easy sell it…etc. etc.
So he will offer you a low price not correct for the stone.
On the other hand, become very difficult sell the stone in this conditions to other people.
Would you buy the stone in this conditions, if someone offer you the tourmaline for 200$ ?
Another way is find a honest cutter and recut the stone. At this point you need another certificate.
I cutted many tourmalines like this and the final result was always good. Here in Italy the retail price for a stone like your is around 60/80 $ for carat.
For a wholesaler is half… 35/40$.
You have two options:
- sell the stone to a wholesaler ( 23 ct x 35= 800$)
- sell the stone to someone that know the value of your tourmaline and want a original and natural gem.
So you can ask 60$ for carat but you can sell the stone with a discount at 45$ ( 45 x 23= 1.000$ and more!)
Imagine a pendant whith your stone…
The light reflection on the facets and the change of color in sunlight… very, very good!
And is also easy to put in pendant becouse of the height.
These are only some ideas for you…
You can think about these options and choose the best for you.
I wish you the best for your life!
Thanks, Luigi
Will you recut this stone for me?
Yes, no problem. Please write your email and I will
contact you privately.
Thanks.
Update,
Luigi from this forum did the recut of this tourmaline. He got a lot of credit for his work from GRS. The tourmaline has become so beautiful, and it didn’t loose much weight - less than 2ct. It is still nearly 25ct.
Luigi suggested to make a pendant with the tourmaline, but I just send the loose stone to an auction house. They were of same opinion, -and the result speak for itself.
From an ugly mans ring to a beautiful pendant.
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