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 Post subject: Help identifying purple gem
PostPosted: Fri Nov 12, 2021 4:51 pm 
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Hi all! I am a geologist who barely passed mineralogy two decades ago, and I need your help. I was gifted this ring by my MIL who stated she bought it "years ago at an antique store" because she likes purple. I'm wondering if anyone can help guide me to what it might be? Here's what I know:

- It's violet colored in sunlight (picture)
- It's nearly colorless in artificial light (picture taken on a plane at night)
- There are no visible scratches on the face of the stone as seen through a 10x loupe
- There are no doubling of facets when observed through the loupe
- The internal facets throw rainbows as often as white flashes

Any thoughts? I did some research and couldn't easily find anything about purple stones that go colorless/pale in artificial light. Thanks in advance!


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 Post subject: Re: Help identifying purple gem
PostPosted: Fri Nov 12, 2021 6:59 pm 
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My first thought whenever I see this sort of color change is that we have stumbled on a vanadium doped synthetic sapphire...an imitation alexandrite which has been available for over a century.
But, the color change you are describing is opposite of what I would expect to see,
In the case of the synthetic sapphire alex imitation the stone should appear more purple indoors with incandescent light sources (try a candle if all your lights are those horrid CFL type) and more bluish outdoors.
As I'm sure you are aware, it has to do with the different spectral power distributions....more blue in daylight; more red when viewed with incandescent lighting.

So, since your mystery stone is not following protocol, we need to do additional tests.
Single vs. double refraction. Happen to have a polariscope? Crossed polars like whats used with thin sections would work.
Look for bubbles with magnification

Alternative possibilities:
Color Change Alexandrite Neodymium Glass very popular in mid-century Czechoslovakia and Bohemia.
Color change Neodymium doped YAG produced in Russia commercially available since the 60s.
Color change cubic zirconia


Any hallmarks, makers marks or stamps on the ring itself?


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 Post subject: Re: Help identifying purple gem
PostPosted: Fri Nov 12, 2021 7:24 pm 
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If the artificial light is, in particular, a fluorescent bulb, then this would pretty much have to be Nd-doped YAG. It is a very unusual characteristic even among the spectrum of unusual changing colors induced by rare earth element impurities.

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 Post subject: Re: Help identifying purple gem
PostPosted: Tue Nov 23, 2021 4:37 pm 
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Barbra Voltaire, FGG wrote:
So, since your mystery stone is not following protocol, we need to do additional tests.
Single vs. double refraction. Happen to have a polariscope? Crossed polars like whats used with thin sections would work.
Look for bubbles with magnification


Hi! I'm sorry for the late reply. I don't have access to a polariscope, but I did a little home set up with a polarized lens cannibalized from a pair of sunglasses and didn't see any obvious changes in the stone as I rotated it through the polarized light.

Barbra Voltaire, FGG wrote:
Any hallmarks, makers marks or stamps on the ring itself?

The only hallmark is 925 FS.

Thank you for your response!


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 Post subject: Re: Help identifying purple gem
PostPosted: Tue Nov 23, 2021 4:40 pm 
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Stephen Challener wrote:
If the artificial light is, in particular, a fluorescent bulb, then this would pretty much have to be Nd-doped YAG. It is a very unusual characteristic even among the spectrum of unusual changing colors induced by rare earth element impurities.


It IS under fluorescent bulb light! I don't think I have any other types of bulbs in my house - is there another type of artificial lighting I could use to confirm?

Also, thank you for your response! I agree that the color change is super unusual - I couldn't find a darn thing online about a color change going this direction.


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 Post subject: Re: Help identifying purple gem
PostPosted: Tue Nov 23, 2021 7:37 pm 
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That's all the confirmation you need. It's a very unusual material!

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