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 Post subject: synthetic quartz inclusions
PostPosted: Fri Feb 29, 2008 12:25 pm 
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Hi,

Hoping Barbra will chime in here as I think she has more experience with ID'ing synthetic quartz than I do. I have an obsession with sleuthing out amethyst synthetic or natural, but haven't really expanded my horizons outside of that.

I have been examining several very large mounted faceted "topazes" for a friend - they are all actually quartz and I suspect they are hydrothermal synthetics given the appearance and provenance.

Color - greenish yellow ("lemon quartz" ?). They show moderate dichroism of two tones through the table; the heavy silver mountings obscure most other orientations so I have not been able to exactly locate the C-axis. One that I brought home to look under the scope at has a hazy look (the stones are quite deep - this one is the smallest at 18mm deep, so a lot of stone to peer into - the others are larger, but not as hazy).

The slight haze turns out to be minute pinpoint inclusions like dust throughout the stone, but not random - they are oriented in sheets at an angle to the table - not able to say that they are perpendicular to the optic axis or oblique because of the mounting as I indicated. I can't resolve them as other than pinpoints even with a doubler. Are these likely to be "breadcrumbs" or otherwise left-over nutrient from synthetic hydrothermal growth?

I have observed breadcrumb inclusions such as Barbra found in the bi-colored quartz which were random and visible at 60x. But, I haven't seen this oriented haze before.

Any thoughts or references welcome. I might look at this with FTIR to see what turns up, but I would be more pleased with myself if I could interpret these inclusions one way or another. I am better at quantifying zircon crystals in corundum....


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 Post subject:
PostPosted: Fri Feb 29, 2008 3:53 pm 
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Hi,

The breadcrumb inclusions are typical for hydrothermal quartz .. from the seed plate in one plane (thick or thin).

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 Post subject:
PostPosted: Fri Feb 29, 2008 4:44 pm 
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Hi Doos,
I am not sure I understand what you mean - I am seeing multiple parallel planes - are you saying there can only be one such plane? Can the "breadcrumb" inclusions be this fine and so evenly dispersed in a plane - that is, pinpoint even with a doubler? I am prevented from determining the C-axis on this stone so I can't determine its exact orientation to a possible seed plate.

Maybe an alternative question would be - has anyone seen this type of inclusion pattern in natural quartz?

The color could be from irradiating colorless quartz - natural or synthetic.


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 Post subject:
PostPosted: Fri Feb 29, 2008 5:49 pm 
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Do the inclusions seem to be orientated veils or ghosts? These could possibly be indications of start and stop growth cycles. Interfaces between old a new growth.
I think this could occur naturally as well as synthetically and be hard to distinguish. It doesn't sound "breadcrumb" like to me.

From your color description, it sounds like Ouro Verde quartz. A variety from Brazil that gets it's color from irradiation.

As an aside that may not apply here, I read a report that observed that either heating or irradiation can be used to create "greened amethyst," or more properly praseolite. According to the report, the heated specimens showed green through the CCF, while the irradiated showed red. Interesting.

Of course there's nothing that I know of that says synthetic quartz can't be irradiated so, not of much use I guess.


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 Post subject:
PostPosted: Fri Feb 29, 2008 6:27 pm 
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JB wrote:
Do the inclusions seem to be orientated veils or ghosts? These could possibly be indications of start and stop growth cycles. Interfaces between old a new growth.

I didn't think of that! I just compared it to a quartz sphere with a nice phantom in it that sits on my bench - the sheets of inclusions are very similar and the size of the "dust" is comparible..... that is, pinpoint and not able to descern any texture to them (I think of breadcrumbs as, well, looking like breadcrumbs). I guess I could be looking at a natural growth feature and my prejudice was getting in the way of being objective. In hydrothermal growth I assume the conditions would be constant enough to prevent phantoms(?).

Still can't say either way, but that was a good point JB and a good jab to a tired brain, thank you... and here my sphere was staring at me all the time.

I think this is why I am not ever going to be an appraiser... I hate mounted stones - all you appraisers make me feel very humble with your skills!


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 Post subject:
PostPosted: Sat Mar 01, 2008 6:33 am 
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Hi,

In hydrothermal quartz the breadcrumb inclusions are in the seed plate which a very thin slab of quartz and the optic axis will be perpendicular to this plane (the plane of the slab c.q. breadcrumbs). Or it will be at some angle to that plane when the thing is twinned .. if I remember correct .. will investigate.

The breadcrumbs can be in multiple layers in a, lets say 1mm, thick main layer (the thickness of the seedplate). Once you seen a rough hydrothermal block of quartz, you'll never forget how that looks.

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 Post subject:
PostPosted: Sat Mar 01, 2008 10:01 am 
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Doos wrote:
In hydrothermal quartz the breadcrumb inclusions are in the seed plate which a very thin slab of quartz and the optic axis will be perpendicular to this plane (the plane of the slab c.q. breadcrumbs).

I wonder if the owner would be too upset if I just cut all this silver stuff off so I can get to the bottom (or rather, the axis) of this. If it didn't have such an inflated price on it, I would buy it for my stone library.

One of my oft referenced papers on synthetic quartz is on the GAAJ site. I have several synthetic amethysts with intact seed plates and have seen plenty of the rough at shows - it is distinctive as you say.


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 Post subject:
PostPosted: Sat Mar 01, 2008 12:12 pm 
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Hi,

The GAAJ page is great and the specific brewster fringes have been investigated many times before by various authors. Although today it is believed that these fringes are not diagnsotic anymore, there is a difference between the synthetics and the real ones with Brazil twinning. The difference is very subtile. You will need to find the optic axis first of course which is not easy in set stones. You might try immersion.
It is also one of my favourite subjects and hopefully one day I can report on it.

The other day (a few weeks ago) I needed to resort to the "shadowing technique" on a flawless rose quartz and it wasn't as flawless as it appeared to be. Maybe you could perform that microscope technique to see what else is in the stone.

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 Post subject:
PostPosted: Sat Mar 01, 2008 12:49 pm 
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Thought you guys/gals might enjoy this "old" ahem, 1955 manuscript.
Some observations included that may address the original question.

Oldies but goodies.


http://www.minsocam.org/ammin/AM41/AM41_598.pdf


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 Post subject:
PostPosted: Sat Mar 01, 2008 1:16 pm 
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Interesting thread, especially since in my 'off moments' I'm grading a couple of kilos of Zambian amethyst rough I bought in Tucson.

I enjoyed JB's link and here's another 'oldie but goodie' that presents an overview (realize it was published in 1998 and things have changed since then!). There's quite a bit about inclusions that might be of interest.

http://jck.polygon.net/archives/1998/01/jc018-160.html

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 Post subject:
PostPosted: Sat Mar 01, 2008 1:37 pm 
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Hi Rom,
Per your link, I see that the GIA decided that $50.00 was a reasonable cost for "batch testing" amethyst for synthetcs. 10 random stones per parcel as I understand it.


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 Post subject:
PostPosted: Sat Mar 01, 2008 10:32 pm 
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I really appreciate all your comments and your links to online papers. I had the R. Drucker JCK one in my files - had actually wanted to see if he had written a follow-up in Gem Market News (or somewhere else) - I only have newsletters back through 2005. The one on phantoms and veils is very interesting in that it describes them both as natural and synthetic events. I am still digesting it.

Going off on an amethyst/ametrine synthetic tangent - you probably already follow the papers listed here - the one on ametrine has some interesting insights to synthetics and causation of color - see photo links in section on synthetic here. It is a good side reference to the G&G Sp94 on ametrine.

I am facinated by the synthetic quartz bloom.... it is so much bigger than most people, especially the public, imagine. In 2006 the figure I heard at GIA for the amount of synthetic amethyst on the market was above 60% - other people tell me it may be as high 80% - without people knowing that it is synthetic. Does anyone have any alternative published figures?

I will try shadowing and immersion on the set stone - but, the setting really is hampering observation of those planes.

There is just nothing prettier than a nice goethite brush off in the corner.....


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 Post subject:
PostPosted: Mon Mar 03, 2008 3:02 am 
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I once used an electron microprobe to determine that the bread crumb inclusions were a Na Fe SiO2. I never could get an exact chemical composition but those were the major constituents.

I do not know if the 3542 cm-1 IR band applies to synthetic citrine, but that material is orders of magnitude less prevalent than synthetic amethyst.

Given your description of the color and the inclusions I'm thinking you have a natural stone.

We can agree that you should cut away that messy silver.

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