Post subject: Re: No luck, identifying this green stone...
Posted: Wed Sep 16, 2020 2:49 pm
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Joined: Thu May 12, 2016 2:18 am Posts: 1542
abeck wrote:
A "just out of curiosity" question. Does fully-metamict green zircon not show dichroism/double refraction, and is it still OTL?
Just something about the odd green color and the bright (internal?) striations seen through the table...
But then y'all have probably seen way more of this kind of stuff...
Zircon was my initial response from color. But lustre is low, the stone is in too good of shape, it should be clearly OTL (even green), and he is seems confident of SR.
In theory yes, a metamict green zircon could decay to a completely amorphous state, have an RI as low as being reported, and become SR. This level of decay would be extremely rare. I don't recall ever seeing one like that in practice.
The break down of the crystal structure required to completely eliminate DR would increase the already brittle nature of the stone. In a old ring like the one being shown where the silver has been abraded, I would expect to see heavily abraded facet junctions, and scratches on the facets themselves. None of this is in evidence in the pictures being shown.
But like I said, possible....
I am sure this stone would be a fast ID in my lab.
Next a Dichroscope, a good spectrum. We could look for the Zircon line. Possibly remove from ring (easily reset in this ring), and get an SG.
Post subject: Re: No luck, identifying this green stone...
Posted: Thu Sep 17, 2020 9:10 am
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Joined: Sat Feb 08, 2020 9:09 am Posts: 73
So, I have been conducting some detective work. Assuming the stone is a) green and b) OTL, I went online to look for possible alternatives. I excluded stones where green was not presented as a color variety, when they were described as “too soft for jewelry”. This is my little list and thoughts (which may be completely wrong).
YAG – unlikely. Due to described UV reaction, spectra and inclusions. Gahnite – unlikely, but the most likely possibility I could find. Uvarovite garnet – highly unlikely, but still possible. CZ – unlikely. Due to lack of described inclusions and UV reaction.
Post subject: Re: No luck, identifying this green stone...
Posted: Thu Sep 17, 2020 12:52 pm
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Joined: Tue Apr 05, 2016 7:58 pm Posts: 1424 Location: San Marcos, CA
I'm throwing in my gemology by image assumption based on all the posts so far. .925 Sterling low cost ring with a Chrome Dioside probably a product of China manufactured 15 or so years ago. Making this assumption based on possible inaccurate RI and SR readings. Can this be eliminated by all the current findings?
Post subject: Re: No luck, identifying this green stone...
Posted: Thu Sep 17, 2020 2:09 pm
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Joined: Thu May 12, 2016 2:18 am Posts: 1542
glhays wrote:
I'm throwing in my gemology by image assumption based on all the posts so far. .925 Sterling low cost ring with a Chrome Dioside probably a product of China manufactured 15 or so years ago. Making this assumption based on possible inaccurate RI and SR readings. Can this be eliminated by all the current findings?
Greg, what you say does make sense just looking at the stone, and the mounting. But for that to be the proper ID, pretty much every measurement, and gemological observation made by the poster would have to be completely wrong.
The RI would have to be much lower around 1.70 - 1.675 instead of 1.78 to OTL
It would have to be DR not SR
It would have Pleochroism
It would likely have weak UV Long fluorescence instead of none
It would have two thin lines at 505 and 508, and multiple chrome lines in the red instead of the brad band he describes at 500 -550
So every reading he took would have to be very far off.
The really troubling thing is that my confidence in the information we are getting is so low that you are as likley to right as any of us at this point.
Post subject: Re: No luck, identifying this green stone...
Posted: Thu Sep 17, 2020 3:23 pm
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Joined: Sun Oct 16, 2005 12:22 pm Posts: 21600 Location: San Francisco
We can presume that the C axis is not perpendicular to the table as it blinks. I see no interference colors in any direction on the Youtube videos. Anyone notice them?
As Greg mentions, I find settings a good clue as to what one might expect to find within them.
Again, what is the refractive index of your RI liquid?
Post subject: Re: No luck, identifying this green stone...
Posted: Thu Sep 17, 2020 3:51 pm
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Joined: Tue Apr 05, 2016 7:58 pm Posts: 1424 Location: San Marcos, CA
And I used the term "Chrome" very freely, as it was a common mass manufacturing marketing naming convention to label all diopside as chrome. Made it sound like it was exquisite somehow.
Post subject: Re: No luck, identifying this green stone...
Posted: Thu Sep 17, 2020 4:13 pm
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Joined: Sat Feb 08, 2020 9:09 am Posts: 73
I can understand how you, as a CG could have a doubts concerning my abilities. I myself would not stake my life on my spectrometer readings (witch btw was not a broad band from 500-550, but a thin absorption line somewhere between 500 and 550), in that I agree with you.
I do not have the necessary equipment to measure SG, or a dichroscope and until I decide whether or not to remove the stone from its setting I can only get RI measurements from the table facets. One observation, if the stone is OTL isn’t pointless to use the refractometer to look for birefringence? Wouldn’t the reading be OTL as well?
According to my refractometer the RI of the RI liquid is 1.781
Post subject: Re: No luck, identifying this green stone...
Posted: Thu Sep 17, 2020 5:50 pm
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Joined: Tue Apr 05, 2016 7:58 pm Posts: 1424 Location: San Marcos, CA
What kind of refractometer do you have? I have a cheap 100$ unit I use to test rough with that came with RI fluid that is not all that good. Can usually get good reading within 1.52 to 1.6 but after that its hit or miss. Our inhouse GG (spouse) only uses the good stuff I think it is like 1.81+-, as used at the GIA. But I scratched the hemicylinder checking rough once so got hand slapped a little.
Post subject: Re: No luck, identifying this green stone...
Posted: Fri Sep 18, 2020 2:26 am
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Joined: Sat Feb 08, 2020 9:09 am Posts: 73
I have a RHG modell CL with a range of 1.3 ~1.81. I'm using the liquid that came with it when I bought it. Probably not the best quality, but it has worked for me. Until now....
Post subject: Re: No luck, identifying this green stone...
Posted: Fri Sep 18, 2020 10:46 am
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Joined: Sat May 22, 2010 2:51 am Posts: 755 Location: South Africa
Perhaps you could add demantoid garnet to your list of possibilities. The stone is not necessarily the original one in the ring. The exposed shoulders look suspiciously undamaged. Last month I handled a very odd demantoid, distinctly birefringent and with multiple lamellar twinning (but under crossed polars it had spectacular interference colours, unlike your stone).
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