Hi,
I would like to start a discussion of identifying spinel. Any suggestions when it comes to faceted? Determining Syn vs. Natural? Apraising the value? Fluorescence in Spinel?
Thanks!
-Daniel
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The IGS has an article on identifying synthetic spinels that discusses comparing RI, SG, fluorescence, and inclusions of red and blue natural and synthetic spinels. Hopefully that can help.
Pedro
IGS Admin
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Thanks you, I have read the article and it is very interesting, but my issue is thst it only covers red and blue spinel, seeing how spinel comes in a variety of colors the information only helps so much.
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Unfortunately, it was very hard to find much specific information on synthetic spinels in other colors. Reds and blues are by far the most popular colors for spinels, whether natural or synthetic. The main spinel article does have information on properties for natural spinels in other colors, but reds and blues still dominate. However, there is a wider range of info on luminescence for various color spinels.
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I am 95% sure that these are all spinel, but my struggle is identifying whether any/some/all are Synthetic or not. I will have to take a closer look at that article. My issue with identifying these is that i dont have access to a microscope, and all my knowledge come from the past 2+ years of self teaching. Their is a gemologist who has taught me a few thing here and their but I only see them twice a year. He is unsure whether they are Spinel or not because he doesn’t have much if any of his equipment when i see him. He has said that they might be spinel, (unsure if they are syn) but he also mentioned that they could be glass, but the RI would suggest otherwise. If anyone has any suggestions about what i could do/opinion about these stones?
The single stone on the scale is 6.5mm
Also, what would a potenial value be on these gems, if they were ID as a natural spinel? Inclusions in the stones are very small and most, if not all of these stones are eye clean. Would it be worth the time and money to have these ID and appraised at a jewelry store?
Yes,
if they are NOT synthetic worth few Hundreds .
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You’re right, fluorescence only proves simply that they are fluorescent… not revealing gemstone species, or if they are synthetic or not.
But, fluorescence does help some. Also, you could begin by trying some simple separation techniques using a strong magnet:
Garnets (like spinel) can be an assortment of colors, their RI’s can overlap, and they’re both singly refractive. However, If any of those stones in your lot can be pulled or attracted by a (rare earth) magnet… they are not (gem) spinel, but likely a garnet. Note: Not all garnets will show paramagnetic susceptibility… this is only a separation technique.
As for synthetic types, it’s clear from the article Pedro attached, you can discern SOME of the flame fusion type synthetics by checking RI . The flux grown types however will match the natural in RI, but effective use of PL (photoluminescence) readings on UV-Vis, Raman, and even some synthetic diamond testers like the EXA EXA™ - MagiLABS can clearly show you natural from the synthetics.
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Thank you for your feedback, I very much appreciate it.
It’s clear that you have a strong scientific background in mineralogy and gemmology. Do you have an advanced degree in the geosciences? I am only an amatuer but am fascinated by igneous geochemistry.
Some of the techniques that you mention are advanced, ie., Raman spectroscopy.
If you have an answer to my question about how Mn3+ activates Cu+2 in Paraiba tourmaline for color, that would be appreciated greatly.
Figured i would give an update. These spinel are infact natural, and I was told they are worth approximately $100 per carat.
Recently I have come across flame fusion Green Spinel in my lab that was being passed off as Tsavorite Garnet. The specimens were faceted and internally flawless. Between CPFs in an immersion cell, the heavy strain pattern of flame fusion spinel was highly visible. I have recently come across Green YAG being passed off as Tsavorite Garnet as well. Words to the wise. 
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