New Mineral Named After GIA’s John Koivula
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 Post subject: Synthetic Quartz
PostPosted: Thu Oct 05, 2006 11:37 am 
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I purchased a parcel of cut citrine of Madeira color. I dont have any reason to suspect they are synthetic but I want to be sure they are natural before I sell them. Is there an easy way to verify their natural origin?

Jason


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 Post subject: separation tests for quartz (citrine)
PostPosted: Thu Oct 05, 2006 12:35 pm 
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hi Brims:

easiest way is to test the RI of your stones if they are citrine they should have an RI: of between 1.544 and 1.553 and a S.G. of 2.66


That is probably the easiest way to find out if you actually have citrine.

You could also test under magnification looking for Nailhead spicules
breadcrumb-like inclusions

hope this helps

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PostPosted: Thu Oct 05, 2006 12:53 pm 
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Synthetic citrine will have the SAME RI and SG as natural.


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 Post subject: citrine
PostPosted: Thu Oct 05, 2006 1:55 pm 
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Hi:

Yup, Barbara is right.

Just goes to show that a "little knowledge " is a dangerous thing. I am guilty of not having looked far enough for an answer. Sorry, for having misled you brims.

Also there is some bad news on using magnification to separate between the two (natural and synthetic).

"if flawless, separation from natural quartz is not possible using standard gemological tests unless the colour is unnatural (e.g., TP blue)"

Thanks

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PostPosted: Thu Oct 05, 2006 5:12 pm 
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The Gemmological Association of Japan has a lab report on separating natural green quartz from synthetic by observing color zoning related to it's crystal habit.
http://www.gaaj-zenhokyo.co.jp/research ... -02en.html


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PostPosted: Thu Oct 05, 2006 5:52 pm 
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As I understand things, it is now pretty well accepted that you can't rely on the Brazilian Law twinning to separate natural from synthetic quartz. The Japanese study seems to support this as they cite color zoning and inclusions to their separation. Here's the GIA release on the subject, which is more general to quartz:

http://www.gia.edu/newsroom/issue/2798/ ... etails.cfm

(Scroll to the "Insider Gemologist" heading)

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PostPosted: Thu Oct 05, 2006 7:42 pm 
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The Gia study states that inclusions and color zoning is used, it's in the second paragraph above the editors note.


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PostPosted: Thu Oct 05, 2006 7:49 pm 
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But they do qualify that (bold):


"So today, the gemologist must rely on the presence of distinct inclusions and/or color zoning to positively separate natural from synthetic amethyst. If confronted with an amethyst without distinct internal features, caution is warranted, and the material should be sent to a gemological laboratory for advance testing, specifically by means of Fourier Transform Infrared Spectrometry (FTIR)."


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PostPosted: Thu Oct 05, 2006 8:05 pm 
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You're right Red, I didn't mean to imply I was disagreeing with you. The GIA release and Japanese Gemo article are pretty much recommending the same process. The only thing the GIA really adds, as MoDo pointed out, is that strong warning.

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PostPosted: Thu Oct 05, 2006 9:45 pm 
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Ok, i've examined all my stones with a loupe and to my untrained eye I see no zoning or inclusions. Does this mean I have no recourse but to send to a lab?

The thing is I have seen plenty of gigantic citrine rough that is practically flawless. Do I need to assume these stones are synthetic until verified genuine by a lab? If so can someone recommend a lab that can do the job without breaking the bank?

Is it safe to assume that most synthetic quartz is cut into calibrated sizes? What about color? Does it come in as wide a range of colors as natural?

Here is a pic:

Image

Jason


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PostPosted: Fri Oct 06, 2006 9:31 am 
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To the best of my understanding, you're stuck sending those stones to a lab to prove they are natural. It's just not possible for someone with standard gemo tools to prove it conclusively w/o natural inclusions or color zoning.

Synthetic quartz comes in any color that natural quartz does, and then some. Syn quartz should heat & irradiate the same way as natural quartz too, so that only makes things all the more complicated. Separation by color just isn't possible.

I've read of kilo-sized parcels of rough being mixed; chunks of syn with natural crystal points of the same color in the same box. Faceters who demand natural stones only cut crystal points or crystal sections with identifiable crystal growth on them, even if they buy in bulk.

I've been told by some wholesalers that the prices on syn quartz and natural quartz are the same, so they typically don't bother even trying to separate the two either at take-in or on sale.

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PostPosted: Fri Oct 06, 2006 10:01 am 
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pt wrote:
To the best of my understanding, you're stuck sending those stones to a lab to prove they are natural. It's just not possible for someone with standard gemo tools to prove it conclusively w/o natural inclusions or color zoning.


Ok, thank you Peter. Now to find a lab!


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PostPosted: Fri Oct 06, 2006 10:12 am 
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I'm interested to know how this turned out for you. I've been told by others that the expense of lab testing is too much in proportion to the value of the quartz.

Does the cost:value ratio work when lab-fees are added in?
Do your customers really care enough to pay a premium for natural, lab certified quartz?

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PostPosted: Fri Oct 06, 2006 10:24 am 
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I certainly would not bother with certification.
Natural citrine is $8-$20 per carat and synthetic is probably the same? I'd sell it saying I believe it to be natural and if anyone finds out something different, you'll refund their money.

If you sell it to someone who actually cares, let them foot the bill for lab reports.


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PostPosted: Fri Oct 06, 2006 11:39 am 
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http://www.gemtechlab.ch/GemTech/Articles/quartz.pdf
Although it is in French, the message is clear: look at the Brewster fringes (as in the GAAJ article).
Maybe someone will translate the whole thing one day.

It is very hard to get your hands on twinned synthetics, so I'm sure most of the synthetics on the market now are still untwinned and will not show the Brewster fringes.
From what I read sofar, the twinned synthetics will show much more crude fringes. But again, it is a tough job to find some for experiments.

The costs of evaluation will certainly not be worth the effort of investigation, but what can I say .. must be a nerd thingy.


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