Post subject: Re: heat treatment of gemstones and fluid inclusions
Posted: Mon Jul 29, 2013 12:20 am
Valued Contributor
Joined: Wed Jun 18, 2008 12:01 am Posts: 370 Location: Easley, South Carolina
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.'
john
_________________ John Atwell Rasmussen, Ph.D., AJP Web: http://handmadeartists.com/shop/rasmussengems Blog: http://rasmussengemsandjewelryllc.blogspot.com/
Post subject: Re: heat treatment of gemstones and fluid inclusions
Posted: Mon Jul 29, 2013 6:53 am
Gold Member
Joined: Sun Jun 28, 2009 9:56 am Posts: 1284
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)
Post subject: Re: heat treatment of gemstones and fluid inclusions
Posted: Mon Jul 29, 2013 8:19 am
Gemology Online Veteran
Joined: Sun Oct 04, 2009 11:18 am Posts: 595 Location: Madrid, Spain
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!
Post subject: Re: heat treatment of gemstones and fluid inclusions
Posted: Mon Jul 29, 2013 11:14 am
Gold Member
Joined: Sun Jun 28, 2009 9:56 am Posts: 1284
now that's a number one gem video
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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