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 Post subject: Kornerupine!
PostPosted: Sun Nov 03, 2019 4:34 pm 
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I recently had acquired a few small parcels of rough, and Barbra encouraged me to share some of the photos and videos I had taken. As such, ta da!

The two parcels. One with stronger more saturated colors, but the other still a pleasing grey/blue/purple.
Image

From my understanding, a new deposit had recently been discovered in Tanzania, and I was happy to acquire some and play around with the pleochroism. A lot of the kornerupine I had seen online were not terribly attractive (dark, brown, muddy) but these were quite a treat for the eye.

The rough I purchased is fairly small (2-3 carats on average) with some displaying quite beautiful dichroism. The large trichroic pieces sold out before I even had a chance :P

Backlit colors
Image

Image

One particular stone, showing yellow through this axis.
Image

And purple when turned.
Image

And the angled view looking uniquely magical (imo)
Image

And the video of it:
https://i.imgur.com/2zyqWVU.mp4

And a video of one showing yellow/green:
https://i.imgur.com/MjetEzy.mp4

Dark field illumination washed out some color, but the green on one axis still looking strong.
https://i.imgur.com/Ln8G6Pc.mp4

Additional photos and microscope videos here: (not wanting this post to hog too much data :) )
https://imgur.com/a/38jldtz


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 Post subject: Re: Kornerupine!
PostPosted: Sun Nov 03, 2019 10:47 pm 
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This mineral is awesome, no? I was fortunate enough to see some of JackTrick's collection and positively identify them with the GemmoRaman as kornerupine.

Has anyone faceted this material? The potential seems award winning.


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 Post subject: Re: Kornerupine!
PostPosted: Mon Nov 04, 2019 1:40 am 
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yes these are very nice pieces.
We also made some CE from these stones if possible.
Most of them a mint green, only a few go into blue or purple direction.

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 Post subject: Re: Kornerupine!
PostPosted: Mon Nov 04, 2019 1:57 am 
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I've been on the lookout for this pleochroic material. It's kind of like some of the really mn-rich kunzites or green-cross-axis tanzanites, with that green-purple pleochroism. I'd love to see how it cut up. I'm a big fan of how some strongly pleochroic axinites can cut up, but these look like they wouldn't mix to brown which is a big plus.

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 Post subject: Re: Kornerupine!
PostPosted: Mon Nov 04, 2019 12:26 pm 
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The dichroism in Jack's specimens is astounding. The green to lavender is just WOW1


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 Post subject: Re: Kornerupine!
PostPosted: Mon Nov 04, 2019 12:28 pm 
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Maybe Lisa Elser would be a good person to consult.
Lisa? Hello?


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 Post subject: Re: Kornerupine!
PostPosted: Mon Nov 04, 2019 12:57 pm 
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Ok that is insanely cool material.

In general for highly tri-chroic material you put the table so your 'best' colour faces up. If you're cutting to mix colours, a port or brilliant style pavillion works. This is a Tanz with all 3 colours visible.
Attachment:
Tanz-G-Trii-2248_thumb.jpg
Tanz-G-Trii-2248_thumb.jpg [ 775.12 KiB | Viewed 334 times ]

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 Post subject: Re: Kornerupine!
PostPosted: Mon Nov 04, 2019 1:39 pm 
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Holy shit! My jaw just dropped to my knees. I have never seen a better job of working with trichroic material.
JackTrick, I think you know where to turn for step 2.


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 Post subject: Re: Kornerupine!
PostPosted: Mon Nov 04, 2019 2:16 pm 
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Stephen Challener wrote:
I'm a big fan of how some strongly pleochroic axinites can cut up, but these look like they wouldn't mix to brown which is a big plus.

Yeah! I've heard the big worry with faceting pleochroic stones is you mix the colors together and (like kindergarten painting) you end up with a muddy brown.

Lisa Elser wrote:
Ok that is insanely cool material.

In general for highly tri-chroic material you put the table so your 'best' colour faces up. If you're cutting to mix colours, a port or brilliant style pavillion works. This is a Tanz with all 3 colours visible.
Attachment:
Tanz-G-Trii-2248_thumb.jpg

Oh my goddddd :shock:

That is *astonishingly* beautiful. I hope my rough can turn out as otherworldly!

I definitely want to get some of this faceted. Currently looking for lapidaries comfortable working with rough this size and experienced with pleochroic material :)


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 Post subject: Re: Kornerupine!
PostPosted: Mon Nov 04, 2019 2:49 pm 
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Barbra Voltaire, FGG wrote:
Holy shit! My jaw just dropped to my knees. I have never seen a better job of working with trichroic material.
JackTrick, I think you know where to turn for step 2.


I made Barbra curse. I’m not sure whether to feel guilty or proud

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 Post subject: Re: Kornerupine!
PostPosted: Mon Nov 04, 2019 5:24 pm 
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We used to get these stones rarely back in the day in East Africa. However, most tended to the green/brown colors.

As Lisa has said, pick your desired dominate color to be face up.

Then cut the stone so as to show the maximum possible amount of color from the other axi. This is the opposite of what you would do with say a tourmaline with a closed, or off color C axis. With such tourmalines you cut the bad axis very steep to avoid as much as possible the color showing up through the table direction. With these you will cut them to the same angles in all directions, and better to a pointed culet rather than a keeled culet.

These look like wonderful examples of Kornerupine. I think they should show their colors very well, and not get the muddy green/brown color so often seen.


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 Post subject: Re: Kornerupine!
PostPosted: Tue Nov 05, 2019 7:02 am 
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Three pics of these vanadium bearing Kornerupines/Prismatines(K/P)...

This mint green variety has no dramatic pleochroism like the chromian K/P...

Except our Raman we love the gem .... :D

Attachment:
46F1D3E6-0295-4D2F-8C09-F275A7183097.jpeg
46F1D3E6-0295-4D2F-8C09-F275A7183097.jpeg [ 45.62 KiB | Viewed 285 times ]


Here compared to Chrysoberyl

Attachment:
FFE0B45D-8A2E-4686-8FD1-4FC78BEA9E20.jpeg
FFE0B45D-8A2E-4686-8FD1-4FC78BEA9E20.jpeg [ 42.94 KiB | Viewed 285 times ]


A group of eastafrican K/P - a deep green chromian bearing stepcut from Burma and two lightbrown/brown from Sri Lanka.

Attachment:
13D86AF3-321D-4A19-AF8D-C7A13B71821D.jpeg
13D86AF3-321D-4A19-AF8D-C7A13B71821D.jpeg [ 43.96 KiB | Viewed 285 times ]


A deep green CE from Burma not pictured.

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 Post subject: Re: Kornerupine!
PostPosted: Tue Nov 12, 2019 7:28 pm 
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I was so excited about this material that I bought...$4,500 worth. Hmm. Oops?

The material is absolutely stunning. The V-mint material is intense with a bluish-green and a lime-green dichroism (the third axis isn't really distinguishable). The Cr-trichrome material is absurd with green, blue, and purple, and comes in both pastels and supersaturated amazingness. Careful planning means you won't mix the colours - check out GIA's basic article on orienting for pleochroism and look at their tanzanite example, and you get a good idea of how to orient properly.

https://imgur.com/gallery/RFJlcqI
https://imgur.com/gallery/m8NiAtU


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