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 Post subject: Blue OTL stone
PostPosted: Fri Feb 02, 2007 2:33 pm 
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Joined: Tue Nov 07, 2006 3:59 pm
Posts: 15
I've got a VERY blue stone - looks like maybe it's colored with cobalt. It is OTL and I'm fairly sure it's SR. How can I tell if it's CZ or YAG or any of the other OTL stones?

When looking up how to differentiate these - they all say the same thing on how to tell what they are - "Test negative with diamond tester, OTL RI reading, gas bubbles possible under magnification" all the OTL stones say the same thing - but that only seems to tell you that you don't have a diamond - not tell you if you have a CZ or YAG or one of the others.

Any insight?

:?:


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PostPosted: Fri Feb 02, 2007 8:59 pm 
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Joined: Tue Mar 14, 2006 11:08 am
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Location: Nashville, TN
Hi Stacyann,
I would first really try to make sure it is SR and not DR. If you feel sure of that then you have just ruled out Zircon and Syn. Rutile. Looks like CZ, YAG and GGG can all come in blue, but blue GGG is more rare and less likely.

These three have different specific gravities (SG). GGG is the heaviest at about 7.05, CZ is about 5.80, and YAG is about 4.55.

In the colorless versions of these stones you can look for the amount of see through they exhibit by turning them table down on some print and looking to see how visible the print is through the stone. YAG has a strong see through effect, GGG moderate, and CZ slight. The strong color of the stone may interfere with this test though.

The amount of dispersion also differs. CZ has strong dispersion, GGG is moderate and YAG is weak. Not sure how much the color will affect your viewing of this but take a look. CZ also has a characteristic orange pavilion flash when viewed looking down at the pavilion. Again, not sure if you will see this with a strongly colored variety.The spectrums also differ.


SG might really tell the tale though if you can get it. Looking in my gem handbook, it says that blue YAG is colored by cobalt. Not sure about CZ.

I hope this will give you a few clues to work with. Let us know what you determine it to be! Cheers-Carrie


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