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 Post subject: Yellow tourmaline (tsilaisite)
PostPosted: Mon Jul 23, 2012 1:31 pm 
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Ok, looking for references on this material. I have a 5.79 slightly greenish yellow and I am wondering about rarity. I have never seen a larger one and most that I have seen are in the 1-2 carat range.

I have seen a couple of stones that were a true yellow with barely any green. Does anyone know if this is a function of more or less Manganese and do the purer yellow qualify for the mineralogical definition of tsilisite?

Any and all wisdom welcome.

R.

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 Post subject: Re: Yellow tourmaline (tsilaisite)
PostPosted: Mon Jul 23, 2012 5:16 pm 
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I'm interested in these questions too. I've acquired a 7.29ct Canary yellow piece that will be going for a recut. Interesting thing about it is that though Malawi is known for canary yellow tourmaline, this piece is said to be from Mozambique.

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 Post subject: Re: Yellow tourmaline (tsilaisite)
PostPosted: Mon Jul 23, 2012 10:16 pm 
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Quote:
Ok, looking for references on this material. I have a 5.79 slightly greenish yellow and I am wondering about rarity. I have never seen a larger one and most that I have seen are in the 1-2 carat range.

I have seen a couple of stones that were a true yellow with barely any green. Does anyone know if this is a function of more or less Manganese and do the purer yellow qualify for the mineralogical definition of tsilisite?
Hi Richard,
I am not able to address the chemical elements of Tourmaline, but having been in east Africa 2 to 3 times each year, I have found only a few truly yellow colored Tourmalines. They were mined in Morogoro TZ. All had a very slight greenish component.

We have one 4-1/2ct emerald cut in stock, from Nigeria. And it too has a hint of green.

Have also faceted numerous golden Tourmalines, mostly from Kenya, but these were true golden's even on the C axis. The largest of the golden may have reached 5cts.

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 Post subject: Re: Yellow tourmaline (tsilaisite)
PostPosted: Sun Jul 29, 2012 11:48 am 
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These were all fairly small as evident in the pictures. All came from Afghanistan and showed a good yellow down the c. Most of the photos backlit to some degree

Image

Image

Image

Image

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 Post subject: Re: Yellow tourmaline (tsilaisite)
PostPosted: Sun Jul 29, 2012 11:55 am 
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As far as causes of color I have a PowerPoint presentation given by the MP2 research group on the "Trace Element Chracterization of Tourmaline from World-wide Pegmatite Locations" [preliminary results]
with Yellow and Brown being
* Ti4+/Mn2+ IVCT
*Fe3+ or Mn2+ content
*Ti4+/Ti3+ IVCT
* Hole traps of type O- in interaction with 2 Al nuclei caused by irradiation

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 Post subject: Re: Yellow tourmaline (tsilaisite)
PostPosted: Sun Jul 29, 2012 12:11 pm 
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The Winter 2007 Gems & Gemology features an article entitled:
Yellow Mn-Rich Tourmaline From The Canary Mining Area, Zambia
Abstract wrote:
The most important source of yellow gem elbaite is the Canary mining area in the Lundazi District of eastern Zambia. The tourmaline has been mined since 1983 from both pegmatite and eluvial/alluvial deposits, in colors typically ranging from yellow-green to yellow to orange and brown; much of the orange-to-brown material is heated to attain a "golden" or "canary" yellow color. The tourmaline is Mn-rich (up to 9.18 wt.% MnO documented in the literature) and contains traces of Ti and little or no Fe. The distinctive composition of this tourmaline is probably the result of the crystallization of abundant schorl from an unusual B-rich, Li-poor pegmatite magma, which depleted Fe while conserving Mn until the late-stage crystallization of gem pockets.

The full article is available for free download:
[pdfview]http://gia.metapress.com/content/c3505q64kq530152/fulltext.pdf[/pdfview]


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 Post subject: Re: Yellow tourmaline (tsilaisite)
PostPosted: Sun Aug 12, 2012 9:50 pm 
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As a true yellow tourmaline aficionado (read:obsessive) I've seen several sources for yellow tourmaline, all of which have their own color / chemical characteristics. The neon slightly greenish-yellow (which are Malawi/Zambian) are hardest to obtain (I have several, mostly under 1 ct). I have seen similar colored material from Nigeria also. Paler yellow can be found on rare occasion in Afghan tourmaline.

"Tsilaisite" by its definition doesn't exist, from what I've been told. So it's not a term generally used. Please correct me if I'm wrong. I was using the terminology till I was told I should only be calling it "canary tourmaline." Fair enough. It describes the stones better anyway. No one knows what "tsilaisite" is except us gem geeks. ;)

There's also a new find of yellow tourmaline in East Africa of which I have a few. They're not canary but by the photo you'll see the difference between this find and the canary stones. They are still extremely brilliant and when cut well amazingly dispersive. The ones below range from 3 to 7 ct. Color-wise they are more of a deep lemon to golden yellow, not sunset tourmaline (far more brilliant, no brown dravite-ish secondary color), with excellent crystal.


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