CIBJO releases Gemmological Special Report: considers process of separating measurable facts from opinion; See Gemological Articles below.
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 Post subject: heat treatment of gemstones and fluid inclusions
PostPosted: Sun Jul 28, 2013 1:42 pm 
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I was wondering, what is the threshold temperature that will cause fluid inclusions in a gemstone to dehydrate thus revealing the treatment?


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 Post subject: Re: heat treatment of gemstones and fluid inclusions
PostPosted: Mon Jul 29, 2013 12:20 am 
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would depend on what the fluid was. however, water reaching 100 degrees C would expand explosively when steam was produced and cause sever fracturing of the mineral structure.'

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 Post subject: Re: heat treatment of gemstones and fluid inclusions
PostPosted: Mon Jul 29, 2013 6:53 am 
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well I suppose a negative cavity inside a gem can handle the steam pressure to a certain degree, doesn't it? (I'm mainly thinking of salty water inclusions)


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 Post subject: Re: heat treatment of gemstones and fluid inclusions
PostPosted: Mon Jul 29, 2013 8:19 am 
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Water passes to vapor at 100 ºC only at standard atmospheric pressure (1 bar). Inclusions cavities are closed systems so when you heat the stone, internal pressure rises and the temperature of liquid to vapor phase change for water rises too. In the example below you have to go higher than 280ºC to get supercritical fluid.

As for decrepitation, you usually have to go even higher, until the internal pressure overpasses the resistance of the mineral structure. The exact temperature will depend on many factors: temperature of mineral formation, the strength of its structure, but also the size and even orientation of the inclusions!

In the samples of emeralds from the Urals, like that one recorded, in some cases I had to overpass the temperature of total homogenization in some 50-100ºC to reach decrepitation, but in other cases some inclusions exploded even before total homogenization. So usually a wide range of decrepitation temperatures can be observed even in the same sample!


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 Post subject: Re: heat treatment of gemstones and fluid inclusions
PostPosted: Mon Jul 29, 2013 8:25 am 
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nice vid, Egor!!! Really well done, thx for sharing!!!! =D> =D> =D> =D> =D> =D> =D>

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albé

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 Post subject: Re: heat treatment of gemstones and fluid inclusions
PostPosted: Mon Jul 29, 2013 11:14 am 
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now that's a number one gem video =D>

my concern is that unlike corundums which are usually treated at high temperatures, most gems (quartz, beryls, topaz, tourmalines, spodumene, apatite...) are color treated at rather low temperatures, like 400 to 600°C, and I was wondering is any dehydrated veils and/or tension cracks would consistently be observed from such low heating? Or is it possible that a 400°C heat treatment would leave fluid inclusions unafected (so that observation of fluid inclusions would not reveal the treatment)?


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 Post subject: Re: heat treatment of gemstones and fluid inclusions
PostPosted: Tue Jul 30, 2013 2:11 am 
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Fabulous video! Thank you Egor!

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