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 Post subject: Yellow stone
PostPosted: Mon Mar 04, 2013 3:33 pm 
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Hey all-
Need a little help with finalizing a stone id. I realize this would be simple if I had a conoscope (that would fit in my mag-lit style polaroscope but I don't). The vital info is as follows:
mean SG: 2.63 (my scale tends to run a smidge low)
mean RI: 1.69 (mine tends to run a bit high)
Bifringence: .006
no reaction to uv, or chelsea filter
repelled by n-52 magnet (so diamagnetic)
stone is a transapernt golden yellow (oY4/3 based on an amature eye and the chart here in Gemology project)
dichroscope shows 2 color/5 reads (yellow/light yellow) uniaxial double refraction
polariscope shows double refraction

I've narrowed it down to golden beryl or citrine, but as I said no conoscope to say weather uni+ or uni - (that would make this whole things too easy :D )

based on my SG it could go either way
RI leads towards beryl
dichroscope could go either way (yellow/light yellow = citrine, yellow/lemon yellow = golden beryl not sure I could tell the difference between light yellow and lemon yellow)
the magnetic reaction leads me to citrine (diamagnetic=repel) unless golden beryl is repelled but my understanding is that it would inert (paramagnetic)

the stone comes from my local coin exchange so the providence is a complete mystery but would lean to citrine more the beryl (The owner loans me the "junk" colored stones to practice identification on. I give him my amature opinion and get experience and he has an idea of what it company gemologist is getting. No money is at stake in the id of said stones.)

any thoughts would be helpful thanks.

Brian


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 Post subject: Re: Yellow stone
PostPosted: Mon Mar 04, 2013 3:53 pm 
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Hey Brian
The RI indicates it is neither beryl nor citrine, unless your refractometer is seriously off. Do you have a known piece of quartz you can check it with? What does it read then?
Expected:
RI Beryl 1.575 - 1.583 + or -
RI Citrine 1.544 - 1.553

Refractive index readings will determine if the unknown is uniaxial + or -.
When you were taking the readings, which number was consistent and which one changed?


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 Post subject: Re: Yellow stone
PostPosted: Tue Mar 05, 2013 4:36 am 
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Re-ran mystery stone and came out with 1.61 for RI. Ran known citrine and got RI 1.538.


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 Post subject: Re: Yellow stone
PostPosted: Tue Mar 05, 2013 10:29 am 
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Just for fun, i run GT Tools pro with those numbers and it says "Calcite"???

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 Post subject: Re: Yellow stone
PostPosted: Tue Mar 05, 2013 1:28 pm 
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The birefringence is totally wrong.
Birefringence of calcite is 0.172

Have you considered it may be biaxial and perhaps it is topaz?
What is the weight of the unknown? Dimensions? Cut?


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 Post subject: Re: Yellow stone
PostPosted: Tue Mar 05, 2013 3:15 pm 
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Here's something I learned from one of my instructors at the GIA. It has come in handy more than once!

Any transparent, DR stone with an RI between 1.60 - 1.65, and an SG higher than 3.32 (should be 3.53) must be topaz.

Brian's SG is too low for topaz, unless he's made an error.

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 Post subject: Re: Yellow stone
PostPosted: Tue Mar 05, 2013 4:54 pm 
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Yeah, something doesn't add up with the data. I agree.


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 Post subject: Re: Yellow stone
PostPosted: Tue Mar 05, 2013 8:00 pm 
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Squeeze it :D :D


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 Post subject: Re: Yellow stone
PostPosted: Tue Mar 05, 2013 9:19 pm 
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Dr. Hanneman's "Squeeze it!" comment isn't implying you should use your yellow stone to make lemonade:
Dr. Hanneman in a previous thread wrote:
Close your eyes and hold the stone behind your back between your fingers and squeeze it.
If it is topaz, it will slip out of your grasp. If quartz, it won't.
Closing your eyes is optional. :D


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 Post subject: Re: Yellow stone
PostPosted: Wed Mar 06, 2013 9:59 am 
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Ok Everyone-
Here is some clarification. Tools: Hannamen refractometer, digital caret scale, oplsstyle spectrascope, calcite dichroscope, minimag version of darkfield and polariscope n52 magnet, 10x loupe, lw/sw uv light and Chelsea filter. With said equipment I have gotten reasonably accurate and repeatable results with my refrence stones of: citrine, Garnet, ruby and CZ. That being said I'm confident that me readings are at least ballpark. So here is all the data I've collected on this stone.

Sample: 022813CEA-2 (1 stone)
Cut: Oval w/ pineapple pavilion
Color: transparent, golden yellow (oY/3)
Weight: 5.65 ct+/-0.05 (water weight 3.50 ct)
Mean S.G: 2.63
Chelsea Filter: inert
Black Light: inert
Magnetism: repel
Dichroscope: 2 colors (very faint)/5 reads = double refraction
Polariscope:ADR, double refraction confirmed
Mean R.I: 1.6x+/-0.01 Birefringence:  0.006
Spectra: no spectra observed
Others: Large fisheye eye clean,  except large chip at table-star meet 10x loupe Rolled girdle, polish good minor chipping and scratches pavilion not quite symmetrical
Darkfield same as above

There is some flux with the RI based on the facet angle used, if I use the pavilion main angle of 50ish degrees then RI is 1.61, if I use the pavilion star at 42, then i get closer to 1.69. I am sure though the RI is at least 1.6x.

So here is my logic:
According to Schumann, there are 17 gems that fall in the yellow color with density of 2.50-2.99 and RI of 1.6-1.699. 18 if citrine is included.
Since the coin exchanges business model assumes any stone that doesn't test as diamond Justin doesn't have any real incentive to be gentle with non diamonds. As such, any stone with hardness <7was eliminated. List of 18, now down to 5. Phenakite is eliminated b/c density is too hi, and wrong pleochroism.
Tourmaline was out b/c density
Danburite was out b/c of density, spectra, and fluorescence
Citrine is out b/c RI. All my citrine and quartz test out at 1.53-1.55, and the image projected by this stone is beyond the 1.54 mark.
Because topaz was mentioned I did think that as well, but it's out because of density, wasn't slippery, no flourescence.

So that leaves Beryl or mystery gem. Since I can't scratch or acid test the stone those are out. But the stone did have a strone repel reaction to the n52 mag. Again if a better than fair guess on the ID can't be made that's fine. This stone will be recommended on to Justin s store gemologist as curious enough to warrent a profesional look.

Hope this added info helps clarify this.


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 Post subject: Re: Yellow stone
PostPosted: Wed Mar 06, 2013 2:17 pm 
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Do you have access to a microscope? Are there any inclusions? Can't Justin's gemologist tell you what it is??

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 Post subject: Re: Yellow stone
PostPosted: Thu Mar 07, 2013 1:25 am 
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no microscope, but couldn't detect any inclusions under 10x or 10x darkfield. Ultimately this stone will go to the gemologist (as kinda wierd) but I may not hear back as to what it is. I id the stones for Justin, for practice and fun. He then pass the info up the chain to the gemologist if he (the gemologist) thinks they are worth the time to look at. Remember their business model assumes that non-diamond stones are fakes.


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 Post subject: Re: Yellow stone
PostPosted: Thu Mar 07, 2013 1:43 am 
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What instruments did you use to determine the SG?


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 Post subject: Re: Yellow stone
PostPosted: Thu Mar 07, 2013 2:24 am 
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hydrostatic method with my digital gem carat scale. gotten good results on my test stones with this scale when i compared with my citrine.


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 Post subject: Re: Yellow stone
PostPosted: Thu Mar 07, 2013 5:47 am 
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Well, you can't just leave us hanging :evil: . Insist (beg, bribe, whatever :P !) that Justin let you know once the gemologist determines the identity of this stone!!

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