New Mineral Named After GIA’s John Koivula
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 Post subject: Identification of Clear High-RI crystal
PostPosted: Mon Jun 03, 2019 5:33 pm 
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I have a boule end of a pulled synthetic on its way to me, but of unknown composition.

I'm told the material in question has a density of ~4.2-4.4 but that's all the information I have.

Any suggestions of other tests to do that might help narrow down the candidates? The RI is well over 1.8 so my refractometer won't be much help.

Thanks!

-Allan

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 Post subject: Re: Identification of Clear High-RI crystal
PostPosted: Fri Sep 06, 2019 9:22 pm 
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Let's just start with classical gemological testing:

-observation of surface features and inclusions under magnification (loupe/microscope)
-in the process, also check for doubling (of broken angles, inclusions and/or surface features),
-confirm exact SG of the material, with two decimals (let's note that a digital scale accurate to 0.01g will work fine provided that the stone weighs at least 3g),
-give a few tries at a spot reading with the refractometer, just to confirm that the material is indeed unreadable (I know it is supposed to be >1.78 and thus unreadable but let's just make sure)
-then see if you can try and get the optical character of the material using polariscope+conoscope (note that a polariscope can be built from a broken LCD screen, and a triplet loupe can be used as a conoscope).
-check spectrum (if any) with handheld spectroscope
-check LW & SW UV fluorescence (if any)
-considering it's a rough, you may also want to check hardness (first try against a plate of copper, if copper gets scratched then try against glass, and if glass gets scratched then try against a polished piece of quartz).

Oh and don't forget to provide us with a clean picture (properly focused, in daylight, over a white background)


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 Post subject: Re: Identification of Clear High-RI crystal
PostPosted: Sat Sep 07, 2019 8:47 pm 
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Or, if push come to shove, knock off a wee bit and send it to me. I'll give it a spin on the GemmoRaman. 8)


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 Post subject: Re: Identification of Clear High-RI crystal
PostPosted: Sun Sep 08, 2019 12:43 am 
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Thanks for the ideas.

SG was about 4.5
LWUV reaction - weak pink fluorescence
Not able to get SG reading at all - even polished a little flat on it. So above 1.8
No reaction in polariscope

After putting all this together, I came to the conclusion it's clear YAG. Too bad, I was hoping that it was Lithium Niobate :D But clear YAG isn't so bad also.

-Allan

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