New Mineral Named After GIA’s John Koivula
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 Post subject: Synthetic Opal Questions
PostPosted: Thu Oct 10, 2019 2:54 am 
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Hi all,

I was given some samples of the synthetic opals by a generous gentleman at one of the Denver Gem Shows. He gave me four kinds of synthetic opals, Gibson, Stellar, Aurora, and GMM. I tried to look for the snake skin of the unpolished Gibson rough but I don't have a microscope. I don't see any snakeskin on any of the synthetic opals. How do I identify each kind of synthetic opals? What are the indications?

I also bought some Brazilian opals from the same vendor. The Brazilian opals I have are semi-transparent. They have the play of colour that look more like aurora or big flashes, not patchy nor pinfire. I took one Brazilian opal to the free Gem ID at the show. The RI was right for opal. They tried to see if the stone can float in the saturated salt water which I think it is not a test for the opal. They have a microscope. They though it was a synthetic. I believe the opal is genuine since the vendor has his own opal mine. What are the characteristics for a Brazilian opal?

Thank you.


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 Post subject: Re: Synthetic Opal Questions
PostPosted: Thu Oct 10, 2019 9:46 am 
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Saturated salt water is a test for amber, which is just a bit less dense than salt water. Opal will never get anywhere close to that low, and putting it in salt water is a bad idea in general, so I would not take their opinions too seriously if they thought that was a reasonable test to try.

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 Post subject: Re: Synthetic Opal Questions
PostPosted: Fri Oct 11, 2019 2:32 am 
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Thanks Stephen. I only know the saturated salt test is for amber. That's why I suspect their conclusion.


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 Post subject: Re: Synthetic Opal Questions
PostPosted: Fri Oct 11, 2019 12:00 pm 
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Here is a little more information on Brazillian opal:
https://www.opalauctions.com/learn/a-z- ... nformation

Can you post pictures of the stones you received from the vendor?

The snakeskin appearance of a "synthetic" opal is directional. When viewed perpendicular to the snakeskin direction the color pattern looks linear.
Courtesy of geminterest.com:
Snakeskin:
Image

Linear cross view.
Image

A looming question remains. Are synthtic opals actually synthetic, or are they imitation?



Also, Nathan Renfro has recently compiled an article on opal, including an opal chart:
https://www.gia.edu/gems-gemology/summe ... opal-chart


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