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 Post subject: No luck, identifying this green stone...
PostPosted: Tue Sep 15, 2020 3:56 am 
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Hello!
Trying to identify this stone has been very confusing! The stone is set in a unmarked silver ring. I'm no expert, but I think the cutting style is relatively early. This because of the small table and unpolished girdle. Please correct me if I'm wrong. The stone messures 11x9x7 mm. These are my results, so far.

The refractometer shows an RI of 1,78 and SR.
However, the polariscope shows The stone as DR (blinks four times).

No reaction to either LW or SW UV light.

In the spectroscope I can see a clear absorption line in the green, about 500-550 nm.

There are inclusions in the stone. The most visible is a reddish brown fingerprint inclusion. There are also visible striations within the stone. I'm sure there is a gemological term for this that I don't know.

As always, I would be most grateful for any thoughts!


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 Post subject: Re: No luck, identifying this green stone...
PostPosted: Tue Sep 15, 2020 10:15 am 
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The color looks so different in the image that looks like it is in the polariscope. Can you rotate the stone in the polariscope and take two pictures if you get two different colors. Note that the polariscope should be set to its brightest (uncrossed) position to do this.


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 Post subject: Re: No luck, identifying this green stone...
PostPosted: Tue Sep 15, 2020 2:07 pm 
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Thank you, and yes I can post 2 pictures. And, a video
https://youtu.be/eykVWLSdKX8
Don't know if I would call it different colors...


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 Post subject: Re: No luck, identifying this green stone...
PostPosted: Tue Sep 15, 2020 6:13 pm 
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Are you sure that the RI reading of 1.78 isn't the RI solution?

What is the ring made out of? Any maker's marks, hallmarks?


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 Post subject: Re: No luck, identifying this green stone...
PostPosted: Tue Sep 15, 2020 7:19 pm 
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I see no dichroism in your pictures. So, likely SR.


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 Post subject: Re: No luck, identifying this green stone...
PostPosted: Tue Sep 15, 2020 9:27 pm 
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Also, the blinking you are observing with crossed polars may be ADR.

May I suggest that you take the RI again starting at the lower end of the scale and moving upwards.


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 Post subject: Re: No luck, identifying this green stone...
PostPosted: Tue Sep 15, 2020 9:41 pm 
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How confident are you in the refractive index reading you gave us? i am always suspicious of readings so close to the 1.81 RI max of most RI liquids. In fact in many countries RI liquids don't go that high.

There are multiple synthetic materials that make sense for this stone as an OTL stone. Pretty much no natural ones.


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 Post subject: Re: No luck, identifying this green stone...
PostPosted: Tue Sep 15, 2020 10:03 pm 
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Quote:
There are multiple synthetic materials that make sense for this stone as an OTL stone. Pretty much no natural ones.


For example?


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 Post subject: Re: No luck, identifying this green stone...
PostPosted: Tue Sep 15, 2020 10:48 pm 
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Barbra Voltaire, FGG wrote:
Quote:
There are multiple synthetic materials that make sense for this stone as an OTL stone. Pretty much no natural ones.


For example?


If the RI is OTL then:

CZ in the dark green colors, most likely the dark peridot color. But can be made by suppliers in almost any color of green.

YAG can also be made almost any shade of green.

Close options are readily available Available at RusGems.

https://rusgems.com/production/cubic-zirconia/

These kinds of synthetics makes sense in silver based on value.

Looking for a high SG might be the next step.

-----------------------------------------------------------------


However, when I look at the images of the stone in the ring, using the luster of the silver to estimate light levels, the luster of the stone doesn't look like I expect a super high RI stone to look.

This is obviously the weakest of evidence. But we are trying to do things with pictures that shouldn't be done that way.


-----------------------------------------------------------------------------


I also can't help but feel that the strain/grain that seems to appear in one of the image has the potential to be significant. But it is curiously missing in the polariscope images. This may indicate it is an artifact of the light rather than a characteristic of the stone.

All such sketchy information to work from. Thinking out loud.................


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 Post subject: Re: No luck, identifying this green stone...
PostPosted: Wed Sep 16, 2020 3:02 am 
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Barbra Voltaire, FGG wrote:
Are you sure that the RI reading of 1.78 isn't the RI solution?

What is the ring made out of? Any maker's marks, hallmarks?


Hello! Thank you for your reply!

No, I, am not sure. I looked at it agian, several time. Started looking at the lower end of the scale, nothing. Either the RI is 1,78 or, perhaps more likely is't OTL.

The stone is set in unmarked silver. Handmade, with tool marks. The ring came in a lott of scrap silver I bought at an auction. That is about all I can tell you.


Last edited by Lunacur on Wed Sep 16, 2020 3:43 am, edited 1 time in total.

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 Post subject: Re: No luck, identifying this green stone...
PostPosted: Wed Sep 16, 2020 3:18 am 
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1bwana1 wrote:
I also can't help but feel that the strain/grain that seems to appear in one of the image has the potential to be significant. But it is curiously missing in the polariscope images. This may indicate it is an artifact of the light rather than a characteristic of the stone.

All such sketchy information to work from. Thinking out loud.................


Thank you for your reply 1bwana1!

The strain/grain is not missing in the polariscope. They just have to be viewed through the table, as when viewed in normal light.

(This might be a silly question, are they able to make synthetic gemstones with fingerprint inclusions?)


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 Post subject: Re: No luck, identifying this green stone...
PostPosted: Wed Sep 16, 2020 9:58 am 
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That kind of zoning is often seen in natural corundum. Especially when viewed down the "C" axis.

Corundum also often has fingerprint inclusions as shown in your image.

The RI of corundum is 1.770, which is not that far off your reading. If you are not an expert at RI, or you are not using a high quality refractometer I suppose it is within the possibility of possible error.

The color and luster of your stone is also typical.

The biggest problem is the SR observation. However, you may be only checking down the "C" axis which is an SR direction. Lets try looking through the side of the stone when checking in the polariscope for both DR, and dichroism. It would also be helpful if you purchased a dichroscope to check with. They are very inexpensive.

Please try again with RI but not on the table. Take 4 RI readings RI on each of 4 table facets, rotate the stone 45 degrees between each of the readings.


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 Post subject: Re: No luck, identifying this green stone...
PostPosted: Wed Sep 16, 2020 10:24 am 
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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...

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 Post subject: Re: No luck, identifying this green stone...
PostPosted: Wed Sep 16, 2020 1:22 pm 
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You are right, I'am not an expert and my refractometer is not of the highest quality. However, I have tested corumdom with it. Both natural (comfirmed by CG. (not the pink one) ) and synthetic. All of them showed basically the same RI results and clear birefringence.
Niether of them showed a RI similar this stone.

I managed to get readings from 3 of the table facetts, same result (RI 1.781 or 1.782) no matter how the stone was turned.

I made a few polariscope videos. Seemed easier than pictures. I would be very grateful for your input!

https://youtu.be/a2DXz9K8iB0
https://youtu.be/wbikN23nez4
https://youtu.be/dVPmhsAxOV0


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 Post subject: Re: No luck, identifying this green stone...
PostPosted: Wed Sep 16, 2020 2:43 pm 
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abeck wrote:
A "just out of curiosity" question. Does fully-metamict green zircon not show dichroism/double refraction, and is it still OTL?

Usually, yes.


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