voce
Ideal_Rock
- Joined
- May 13, 2018
- Messages
- 5,178
It sounds like you picked up a great deal. Sometimes people selling them don't know what gems are worth. However--I wouldn't trust the certificate too much, since it might be faked. In some countries labs can be bribed to issue reports stating gems/jewelry is authentic. Or, if it's a less reputable lab, it could just be that the lab had gotten it wrong. According to Wikipedia, for example, demantoid garnet is "Single Refractive", so if your gem is doubly refractive it's not a demantoid. I trust this information is correct, because AJS Gems, a reliable vendor, has this:Thanks for the reply.
I did look into it, and it appears that there aren't synthetic demantoids. It's easily picked up by a small rare earth magnet, which should rule out a lot of substitutes like YAG. Also the certificate indicated anomalous double refraction, which in an isotropic mineral is an indicator of metamorphic shear stress. With that and the gemologist not suggesting otherwise, I'm pretty sure it's real.
Are there other factors a person should look out for with colored stones? I'm a geoscientist by training so I should be able to understand even a technical explanation, but I know nothing about what makes gems valuable to worthless besides the "4 C's".
https://www.ajsgem.com/articles/gemstone-refractive-index-definitive-guide.html
If you were to show me that picture of the gem and have me guess, I would not have guessed demantoid. I would have thought tourmaline.
https://www.ajsgem.com/articles/russian-demantoid-garnet.html
If you Google demantoid garnet, you'll see a ton of pictures of demantoid, all of which look different than the stone that you posted.
Specific to demantoids, they typically exhibit some horsetail inclusions under magnification. I would suggest you check out your gem yourself for specific gravity, refractivity, and horsetail inclusions under 30x magnification.
What makes gems more valuable or less valuable really varies depending on which colored stone it is. I recommend Richard Wise's book Secrets of the Gem Trade, as he writes about the qualities gem dealers look for, for each different type of gemstone. From that book, I also learned that most colored gemstones are doubly refractive, including tourmaline. If it's tourmaline, you still have got yourself a great deal, since your gemstone looks clean and vibrant.