Hi everyone - got a puzzler here which I would appreciate some help with.
I recently got a parcel of colour-change garnets that go from greenish/bluish in 5000k light to pink/red in 3000k. These are some of the odder ones that got me wondering if they are garnet after all.
They look unusual when rotated - the colour intensity changes quite suddenly rather than gradually - and appear to be dichroic, though looking through my dichroscope I do not see obvious dichroism. I'm now questioning my eyes and sanity.
Stone ct SG RI Magnetism A - 2.30ct - SG=4.18 - RI=>1.81 - magnet picks up B - 4.17ct - SG=3.97 - RI=1.76 - magnet drags C - 5.81ct - SG=3.95 - RI=1.77 - magnet drags D - 6.78ct - SG=3.92 - RI=1.76 - magnet drags
My eyes and refractometer skills aren't good enough to get any better numbers (I was cursing most of the time trying to see the damned shadow lines!). And stone A nearly drove me mad until I realized I had a stone over the RI ability of the refractometer
So, from the info I've got, and assuming that they are not dichroic - garnet seems likely. Any other ideas? Any other tests recommended? I can post phone videos also, but I have no idea how to resize them from 1080p to something more reasonable...
Thanks!
-Allan
Pics of the stones in various orientations (5000k light) below: Stone A:
Stone B:
Stone C:
Stone D:
_________________ Allan Aoyama http://www.omnifaceter.net <- Omnifaceter is back online!
Joined: Sun Oct 16, 2005 12:22 pm Posts: 21602 Location: San Francisco
This looks very similar to the spessartite beads I recently purchased at a show. They are from Tanzania. With the polariscope: ADR. Magnetic attraction: some get picked up, others drag.
Thanks for the feedback! I never thought garnets would show umbasara effect, but now I've learned a few things! One of which is how much I dislike using a refractometer
On the polariscope it shows blue to red change depending on the polaroid positions. Interestingly, the thicker areas always show red - lending strong support to the umbasara effect argument.
Double-checking with the dichroscope there is no dichroism that i can see...
So... I think the verdict is cc garnets (some go blue to red, some green to red, some purple to red...) with umbasara effect messing with me.
They are all from Tanzania, so possibly could be from the same find as the beads Barbra posted earlier.
Thanks everyone, I'm feeling a bit better that my gem id skills are not a complete wash
-Allan
_________________ Allan Aoyama http://www.omnifaceter.net <- Omnifaceter is back online!
I’ll try to figure out how to post videos of the stones. The videos show how quickly it switches or intensifies to red, faster than I’d expect just from rotating the stone.
-Allan
_________________ Allan Aoyama http://www.omnifaceter.net <- Omnifaceter is back online!
Some more clues, but I'm still not sure what to make of this all. Stone A is clearly different from the other stones B, C, and D which are all very similar in colour and properties.
Sorry, my videos are all from my iphone in .MOV format and are uploaded to my personal server. Most people will have to right-click the link and download the file, then use VLC or something like that to play the file.
I've re-uploaded stone A - something was wrong with the file.
Here's the stone specifics again: Stone ct SG RI Magnetism A - 2.30ct - SG=4.18 - RI=>1.81 - magnet picks up B - 4.17ct - SG=3.97 - RI=1.76 - magnet drags C - 5.81ct - SG=3.95 - RI=1.77 - magnet drags D - 6.78ct - SG=3.92 - RI=1.76 - magnet drags None of the stones display any dichroism through a dichroscope.
I don't have a spectroscope so can't check the spectrum... maybe next purchase!
Barbra - I'd appreciate if you'd run it through the Gemmo... please PM me where to send and I"ll send you some samples.
They definitely have me baffled!
Thanks everyone
-Allan
_________________ Allan Aoyama http://www.omnifaceter.net <- Omnifaceter is back online!
I don't know much at all about color change gems but that is really beautiful. the color is phenomenal under both types of light and the change looks to be complete. If you don't mind me asking how much was that gem or did you literally pick it up off the ground?
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