Inclusions in Natural, Treated, Synthetic, and Imitation Opal

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PinkDiamond
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Inclusions in Natural, Treated, Synthetic, and Imitation Opal

Post by PinkDiamond »

Here's another one from GIA on inclusions in opals from natural to treated and synthetic. There are galleries of photos of all sorts of opals in the article, and they some some impressive Virgin Valley patterns and inclusions, along with an assorted variety of opals. I would post a few favorites for you if there were links to them, so use the link to view them. I think you're really going to enjoy this one. :!:

Inclusions in Natural, Treated, Synthetic, and Imitation Opal
Nathan D. Renfro, John I. Koivula, Jonathan Muyal, Shane F. McClure, Kevin Schumacher, and James E. Shigley

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Play-of-color is the defining characteristic of gem opals. While play-of-color can be quite spectacular under magnification, as with the roiled green patterns seen in this crystal opal, other microscopic features are often found if one takes the time to look. Field of view 9.60 mm. Photomicrograph by Nathan Renfro.

[i]"When gemologists think of opals, play-of-color is almost certainly the first characteristic that comes to mind (figure 1). While play-of-color patterns can be extraordinarily beautiful under magnification, opals often contain a vast array of spectacular microscopic features in addition to this phenomenon. In continuing G&G’s series on inclusions, this chart will focus on natural, treated, synthetic, and imitation opals.

There have been significant developments in the opal industry in recent years with the discovery of opal from Wollo Province in Ethiopia (Rondeau et al., 2010). This deposit produces opals that contain a wide range of interesting inclusions such as fossilized plant material. Opals from Australia also have the potential to showcase spectacular inclusion scenes, from pyrite crystals to black plumes of manganese oxide that stand out in high contrast to the play-of-color phenomenon. Other sources of natural opal that contain visually striking inclusions are Mexico, the United States, Honduras, and Peru.

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Natural opals can occasionally display amazing colors and structure patterns that are the result of their geological history of formation.

Along with the new Ethiopian deposit came new treatments. The opal from this deposit was hydrophane, which meant it would readily absorb liquids. Soon gem treaters took advantage of this property and began to dye Ethiopian opal a myriad of colors, most notably purple (Renfro and McClure, 2011). This material also proved quite responsive to smoke treatment, which gives it a dark bodycolor (Williams and Williams, 2011). Other traditional opal treatments include color modification by sugar treatment and clarity enhancement by hiding fractures and cavities with resins or oils (Renfro and York, 2011).

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When examined under the microscope, certain visual features, such as those shown here, are good indications that an opal has been treated to improve its appearance or durability.

One of the more prominent opal imitations was introduced in the early 1970s by John Slocum of Rochester, Michigan. In this imitation, thin sheets of metal foil were embedded in glass to produce thin-film interference colors resembling “play-of-color” in natural opal. In 1972, Pierre Gilson began to manufacture a true synthetic opal (Gübelin and Koivula, 2005) that did not require polymer impregnation. Synthetic and imitation opals have been produced over the years by other manufacturers including Kyocera, Almaztechnocrystal, and Openallday Pty. Ltd, but the most recent development is an opal-like plastic manufactured by Kyocera and others in Japan (Renfro and Shigley, 2017). This new material is 80% plastic and 20% silica. It can be produced in large sizes, giving rise to industrial applications such as use in eyeglass frames and watches.

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Synthetic and imitation opals commonly show features resulting from their formation that differ in appearance from those seen in natural opals.

While the images in the accompanying wall chart are by no means comprehensive, they do represent a wide variety of the micro-features one might encounter in natural, treated, synthetic, and imitation opals.

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This chart contains a selection of photomicrographs of natural, treated, synthetic, and imitation opals. It is by no means comprehensive. The images show the appearance of numerous features a gemologist might observe when viewing opals with a microscope.
https://www.gia.edu/gems-gemology/summe ... opal-chart

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SwordfishMining
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Re: Inclusions in Natural, Treated, Synthetic, and Imitation Opal

Post by SwordfishMining »

I'm so glad they included four of the structural patterns I admire from here. The GIA also definitively states wood inclusions that we always said were roots going thru the silica gel. Good plume off plume pics, but it was not the stars & the perfectly replaced cell structure wood with a black matrix I love. For the best result i preserve break faces if possible because opal breaks thru the best color half the time. Polishing to it you dont get quite that much "face" for the wood. The stuff is for sale pretty commonly at gem and mineral shows from the diggers or dealers that all have this place wedged in their hearts. But for some reason the dried woods are not there...hmmmm?
And its not just any thousand dollars if you are buying say 7 pound chunks and thats why people still have the rough for sale or wear it. My friend Gene Sharp went to his grave without a serious offer for his umpteen pound solid blue conk from Rainbow Ridge, it was multi color but blue is rarer.I If people are willing to buy the dry for what is asked, there could be a lot more out there. ie mining. I remember sending email back and forth over some allusion there was no gemstone opals from Virgin Valley, when their own students donated materials for archive samples along with gemstones polished and not crazed. It does make jewellery & last if you know how to pick them or to treat them. I'm proud we got so many pics because thats mainly why people never cut their finds.
Collectors want that fossil specimen as is. Cut the chunks we say mining or sell it as craft supply or potch if it dries uncutable. Putting it back in water does not make it go back clear or hide the cracks much if thoroughly dried first. The insides and outsides or areas usually differ in the way our opal formed too and resin wont cure that. That is why so many people will not gamble on the destruction of natural beauty to "see" if it can be "cut to make a buck" when the odds are against it. If it dried it is on their own shelf or wheels. Now if people were to offer 5-10 times as much for it as they do Australian blacks, diggers would put up with those losses for the money and the refuge would be shut to mining real fast by the NWR. But why lose your "pet" just so someone else can bad mouth it and say it will still crack, never buy that as they languish in the case, in the sun does not do much except melt the cases off the stones too. Thats a pain having to keep putting your opals in unmelted gemboxes. Once this stuff is dried and cut etc, its rarely cracked let alone ever crazed again. Thats what you get from lumber turned to gems or properly cured rough. It goes small, what can we say? Pure opal has always been a buying gamble related to the size of the ante which is why lightning ridge was so favored being chunky, tough and mined the most out.
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SwordfishMining
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Re: Inclusions in Natural, Treated, Synthetic, and Imitation Opal

Post by SwordfishMining »

PS: You KNOW I'm buying this for my house. $40.02 US with tax and shipping.
I'll jump over my shadow. https://www.virginvalleyopal.com"
Opals & more at my ESTY store https://swordfishmining.etsy.com"
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OpalSpectrum
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Re: Inclusions in Natural, Treated, Synthetic, and Imitation Opal

Post by OpalSpectrum »

wow awesome photos ! thanks Pink for sharing
this is something I was trying to do but don't have good enough equipment to shot super macro
although I did some cool macro pix which I didn't posted yet
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