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 Post subject: Stone in question
PostPosted: Fri Oct 09, 2020 12:29 pm 
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Howdy, Folks!

A client brought in a large gem her husband (since deceased) gave to her, no idea what it is.

RI OTL, moderate dispersion.

Moderately doubly refractive (facet lines doubled when viewed thru stone), along the lines of peridot for intensity.

Does not show dichroism - strange!

Gem shows damage where it has been dropped, more what you would see on a soft to mid hardness stone.

Perhaps of more help for some, the spectrum (diffraction) shows a strong wide band in the green, and strong double lines in red, plus a faint band in yellow.

A couple negative crystal inclusions, plus a zone of aligned silky needle blades.

From gem cutting experience, this looks like sphalerite, zincite, scheelite - some of the other softer collector gems but our GIA ID book doesn't go there. Has the brightness and color like an orange CZ (but DR). Has density similar to topaz...

Someone took the time to do a decent barion cut on it, but struggled with finer meets and the finish in some areas. Not some commercial cutting job.

12.14 x 10.18 x 7.84 (deep)mm, 12.30 ct

Sorry about the sparse facts, but it is trying to ring a bell in my memory, wondered if anyone else might find it familiar...


Attachments:
Yanke stone.jpg
Yanke stone.jpg [ 72.61 KiB | Viewed 402 times ]

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 Post subject: Re: Stone in question
PostPosted: Fri Oct 09, 2020 4:15 pm 
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My first thoughts were exactly the same as yours. Have you considered orange sphene?

If you want to send it to me, I'll test it on the Gemmoraman. Cost: return shipping.


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 Post subject: Re: Stone in question
PostPosted: Fri Oct 09, 2020 6:30 pm 
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Looks, and reads, a lot like unheated (based on spectra) honey colored Zircon to me.


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 Post subject: Re: Stone in question
PostPosted: Fri Oct 09, 2020 11:49 pm 
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Zircon could makes sense. Facet doubling is profound.
I took this pic of zircon some years back:
Image

Doubling of back facets with sphene looks about the same.

If we can trust that the SG is close to topaz (3.4-3.6), zircon is too high (4.6–4.7)
Sphene's SG is 3.4 to 3.6


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 Post subject: Re: Stone in question
PostPosted: Sat Oct 10, 2020 12:37 am 
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Barbra Voltaire, FGG wrote:

Doubling of back facets with sphene looks about the same.

If we can trust that the SG is close to topaz (3.4-3.6), zircon is too high (4.6–4.7)
Sphene's SG is 3.4 to 3.6


Spectra sounds about right for some forms of Zircon.

I am not sure where he got his density estimation. When I plug his dimensions into my weight estimation formulas Topaz comes out under 9 carats. Zircon comes out very close to his weight in the 12 carat range.

Zircon still seems to be the likely answer to me at this point.


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 Post subject: Re: Stone in question
PostPosted: Sat Oct 10, 2020 1:28 pm 
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Might be zircon, might not.


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 Post subject: Re: Stone in question
PostPosted: Sat Oct 10, 2020 2:17 pm 
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Barbra Voltaire, FGG wrote:
Might be zircon, might not.



Yep won't know until properly tested.


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 Post subject: Re: Stone in question
PostPosted: Sat Oct 10, 2020 2:21 pm 
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Some more info...

Fluorescence - LW weak yellow green. SW red (?)

Also, here are some of the inclusions, @ 60X

I would ignore the spectrum - I haven't been able to duplicate the image.

One interesting possibility, synthetic zincite (?)

Zircon? Not dichroic.


Attachments:
LW UV 1 600.jpg
LW UV 1 600.jpg [ 25.05 KiB | Viewed 325 times ]
SW UV 600.jpg
SW UV 600.jpg [ 22.44 KiB | Viewed 325 times ]
Incls 60x 600.jpg
Incls 60x 600.jpg [ 19.01 KiB | Viewed 325 times ]

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 Post subject: Re: Stone in question
PostPosted: Sat Oct 10, 2020 3:26 pm 
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Sphene fluoresces orange/red with SWUV; LWUV inert
Inclusion scene: Straight rows and/or "feathers" of tiny crystals. Actinolite needles.

Syn. zincite: density: 5.64 – 5.68

Did you actually test for SG?

I'm a big supporter of Occam's razor.


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 Post subject: Re: Stone in question
PostPosted: Sat Oct 10, 2020 8:30 pm 
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Zincite is soft. Hardness 4.5.
Do you dare?


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