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 Post subject: Re: Bi-color tanzanite?
PostPosted: Sat Nov 10, 2012 10:53 am 
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ELVIS PRASIOLITE...

Understood my friend...I misread allot of things...

Some things get taken personal so that's why I closed with this:

"But I am the suspicious type so interpret this accordingly"...

Regarding the Pink Zoisite I'm not sure about the color being natural or treated??..Haven't seen anything regarding that as yet...

Also the Green Zoisite...For all I know this could be a natural occurring transparent variety of the translucent/opaque Zoisite that's frequently associated with Ruby??...However seeing the bi-color Green/Blue leads me to be suspicious that it is not??

I will look or if anyone has that info please share it...


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 Post subject: Re: Bi-color tanzanite?
PostPosted: Sat Nov 10, 2012 11:25 am 
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Cut ThroatTraders wrote:
Regarding the Pink Zoisite I'm not sure about the color being natural or treated??..Haven't seen anything regarding that as yet...

Also the Green Zoisite...For all I know this could be a natural occurring transparent variety of the translucent/opaque Zoisite that's frequently associated with Ruby??...However seeing the bi-color Green/Blue leads me to be suspicious that it is not??


You are not seeing anything on these topics because you are not following the literature. :smt112
G&G Fall 2012, Gem Notes, reported on naturally occurring pink zoisite, without treatment being mined in the Meralani area of Tanzania.
Image

And as stated in a previous post, I would be happy to send you a pdf copy of the GIAs report on transparent green zoisite mined in Tanzania, mineralogically unique from the massive green zoisite associated with ruby.


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 Post subject: Re: Bi-color tanzanite?
PostPosted: Sat Nov 10, 2012 12:59 pm 
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Barbra Voltaire..

Your right...I fall behind with no excuses...

Please send that report...


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 Post subject: Re: Bi-color tanzanite?
PostPosted: Sat Nov 10, 2012 11:46 pm 
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Done. :D


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 Post subject: Re: Bi-color tanzanite?
PostPosted: Sun Nov 11, 2012 7:05 am 
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So this is very rare and prolley very expensive??

Quote:
only a few random pieces of transparent gem quality pink zoisite have been found in Tanzania. A few
pieces of transparent yellow tanzanite have also been seen from Merelani


Now here is something to sink the teeth into:

Quote:
Faceted violetish blue tanzanites tend to be flawless,
because most inclusions that could fracture the
stones (due to varying thermal expansion) during heat
treatment are removed in the cutting process.

Because most of the green tanzanites are not subjected
to heat treatment, virtually all of the samples
studied-both rough and cut-contained some type
of inclusion.

Multiphase inclusions;
possibly graphite, zircon(?);
unidentified "needles";
growth tubes


It's interesting to note that many of these types of inclusions would show damage after heat...It's also interesting to note that if a very clean faceted violet/blue Tanzanite is being offered as "Unheated"...........Suspicion???

I would be interested to know from those who buy and treat their own Brown Zoisites if they are experiencing internal damage that must be removed during cutting???...Is your rough included???....It was pointed out that:

Quote:
However, the following have been identified petrographically
as inclusions in zoisite: rutile, sphene,
xenotime, diopside, quartz, and tremolite


But if your buying very clean rough it's possible that your not experiencing this heat damage effect...It's also possible I suppose that the Green variety of Tanzanite is more heavily included due to the elevated Chromium content??

Now the following is why I'm so............Suspicious...LoL!!!

Quote:
Prospective buyers should beware, however, as recent
parcels presented as green tanzanite have included
tsavorite, chrome tourmahe, apatite, glass, and YAG,
all of which may be separated from green tanzanite by
the simple use of a dichroscope to verlfy the latter's
trichroic colors.


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 Post subject: Re: Bi-color tanzanite?
PostPosted: Sun Nov 11, 2012 9:44 am 
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NOT pertaining to or directed at anyone's business...

Revisiting Our B-Color Tanzanite upon further review....This may open one huge can of worms but due to my interest in heat treatments and market awareness I will proceed...

1st...This gem appears very clean according to it's listing..."Eye Clean"..

2nd..
Quote:
Color Description : medium light bluish violet
: light strongly yellowish green


3rd..
Quote:
Those stones that are yellowish green
or bluish green in color-and, therefore, contain varying
amounts of chromium-may have occurred in
the zone between the shallower, vanadium-rich veins
that host the violetish blue tanzanite and the deeper,
chromium-rich veins that contain "pure" green tanzanite


4th...
Quote:
Of the stones available, only
approximately 30% are pure green (with no noticeable
modifier), while another 30% are bluish green and
the remaining 40% are brownish green to yellowish
green.


5th..
Quote:
The violetish blue color commonly associated with
tanzanite is usually the result of heat treatment, at
approximately 500°C, of zoisites with strong brown
to yellow modifiers (that is, the conversion of V3+ to
V4+


6th..
Quote:
Specifically, tanzanites that showed bluish green
to brownish green responded to heat treatment by turning greenish blue. This corresponds to the response reported by Schinetzer and Bank (1978-79) for bluish green zoisites with nearly equal mounts of chromium and vanadium.


7th..Groups III-IV-n-V responded to heat as follows:

Greenish Brown/Yellowish Green/Dark Bluish Green transformed to
Light Bluish Green/Yellowish Green/Dark Greenish Blue

Yellowish Brown/Purple/Medium Brownish Green transformed to
Light Blue/Light Purple/Medium Greenish Blue

Yellowish Brown/Purple/Medium Greenish Brown transformed to
Light Blue/Light Purple/Light Greenish Blue

8th..
Quote:
Even though our research showed that dark bluish
green to medium brownish green tanzanites will
respond to heat treatment, our experience is that
such enhancement has not been routinely practiced
on such stones thus far because of the rarity of the
green color and the risk of damaging stones that have
inclusions.


9th..Speculation: Upon seeing a rather dark yellowish/brownish green to possibly greenish brown Zoisite (Bi-Color) that was very unattractive the owner subjected the rough to heat to see if he could raise it's value...Consequently a color transformation to "medium light bluish violet and light strongly yellowish green (Bi-Color) was achieved...This would correspond to the findings of the report by "il. R. Barot and Edward W. Boehm"...Namely that color transformations became lighter and a "bluish violet" was achieved...

10th..It's unknown who the owner of the green Tanzanite was who may have subjected the rough to heat and if this was prior to or after the sell of the rough....Or if in fact that heat was as a secondary event by nature...Problem is unless an inclusion can be used to identify the polished Tanzanite as "Unheated" one would have to remain suspicious as per this:

Quote:
Virtually all of the gem material found is sold in rough form through the leaseholders, who have been issued a Master Dealer's license by the Tanzanian government.


Quote:
Government permission must be obtained to
gain admission to the mining area. For the most part,
foreign visitors are not welcome by local miners.


Of course not...Out of sight out of mind!!!

Figure 16 shows a rather ugly dark brownish green Tanzanite rough that was heat treated to a beautiful light blue...It's rather obvious that the heated rough looks much nicer so unless there was a huge demand for that brownish green I as a burner would teat it...

Again I'm the highly suspicious type as result of exposure to.....Let's just say "Highly Intelligent Trickery" amongst both burners and marketers alike so ____________!!!


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 Post subject: Re: Bi-color tanzanite?
PostPosted: Sun Nov 11, 2012 11:54 am 
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I have a chunk of pink zoisite close to one kilo in weight. Found in Norway, opaque and called Thulite as a trade name... :) Had it for decades.

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 Post subject: Re: Bi-color tanzanite?
PostPosted: Mon Nov 12, 2012 4:37 pm 
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I've some Italian stuff as well:
http://www.gemologyonline.com/Forum/php ... hp?t=10930
My "pink tanzanite"... :lol:


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 Post subject: Re: Bi-color tanzanite?
PostPosted: Tue Nov 13, 2012 1:48 pm 
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Cut Throat, I buy rough tanzanite, both in Arusha Tanzania and from Dealers of rough here in the US. While natural blue stones are not common, I see them in various degrees when going through parcels of stones.

This stone is one I bought in Tanzania that is a natural blue, no heat.

Image

Normally Tanzanite is heated after cutting, but some people will heat it before, with the idea of letting it fracture or crack first, then work with what you have. This also gives you a better I idea of how to orientate the stone. I have always heated after cutting, trying to cut away and inclusions that could grow from the heat.

In my experience, I have heated stones that have been loupe clean that have fractured from the heat, and have heated stones with some inclusions that survived the heating with no further growth.

Looking at rough unheated tanzanite with a dichroscope is fascinating. Almost every piece is different, and you see all kinds of colors. One axis may be root-beer color, another blue, another gray or green all in the same stone.

Since there is no real premium for natural blue over heated stones, I see no reason for anyone to purposely misrepresent their goods.

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 Post subject: Re: Bi-color tanzanite?
PostPosted: Tue Nov 13, 2012 2:05 pm 
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Cut ThroatTraders wrote:
However seeing the bi-color Green/Blue leads me to be suspicious that it is not??

I will look or if anyone has that info please share it...


I would suggest going right to the source. David Weinberg at www.multicolour.com I'm sure David would be more than happy to answer your questions. :)

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 Post subject: Re: Bi-color tanzanite?
PostPosted: Wed Nov 14, 2012 11:13 am 
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Precision Gem....

Thanks for the info:

The clean rough that fractures may be due to internal stress??...A Tanzanite which went threw secondary heat by nature may have been under enough pressure that these stresses would not have damaged the rough??..This could also apply to inclusions which do not show the same damage as in the case of lab treated material??

Mine Geology is an interesting study and I would like to go deeper into it...As it is I have only scratched the surface...With any secondary heating event there is a "Heat Effected Zone" whether Geothermal or Hydrothermal...Thus we would expect to see pockets of heat treated rough where each specimen has been effected rather than treated material scatted amongst untreated material...

In these types of events the rise in temperature may be very slow...Prolonged with very slow cooling...This may also contribute to less damage as the material may actually become stress relieved...Also with some gems such as corundum virtually the same effect can be accomplished at lower temperatures over longer periods of time...I don't know if this would apply to Zoisite??


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 Post subject: Re: Bi-color tanzanite?
PostPosted: Fri Dec 07, 2012 2:12 am 
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Remember my ole 41ct tanzanite crystal that was used(and I was paid for mind you [-X ) by our favorite gemologist, R. James, for a report given at..was it 2009 Tuscon show(2010 maybe?). All the info I have on it as well as other pics of it reside on my desktop..which went down... again 2 weeks ago... for the second time this year.


Attachments:
tanzy 1.jpg
tanzy 1.jpg [ 36.17 KiB | Viewed 2220 times ]

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 Post subject: Re: Bi-color tanzanite?
PostPosted: Fri Dec 07, 2012 11:17 am 
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That is a beauty! :shock:

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