I agree with the people who said sphene (titanite). A little brighter light would help, as a clean, well cut sphene tends to disperse multi-color like a diamond. I have one in a pinky ring and people always comment on it and want to know what it is.
I think the high dispersion is more interesting than the R.Iā¦ garnet (even topazolite) does not have that high of dispersionā¦ you have a real rainbow of colors coming out of the gem. Nowā¦ I have cut some āantique glassāā¦ old Pb-glass that is exactly the same color and looks very similar (it is suppose to have a high RI valueā¦ I havenāt measure mine for same reasonā¦ my refractometer doesnāt go above about 1.80ā¦ but it does have the righ dispersion and the right brilliance. I you put it under a polariscope (or just between two sheets of polarized filmsā¦ and it stays dark as you rotateā¦ then it is probably antique glass ā¦ garnet would do the same as it is isometricā¦ both sphene and zircon will āblinkā light and dark every 90-degrees of rotation. That might help with the ID.
Itās either a yellow zircon (probably), sphene or sphalerite IMO. Is it doubly refractive? If so, definitely not a garnet, which is single.
This looks like Sphene to me. If it is sphene you are lucky to have such a large size. Itās beautiful.
Hello again and thanks for all your replies. I look carefully but I do not see any doubling so as someone mentioned do a specific gravity test so I did multiple times just using a three place balance and came up with 3.795 which maybe Andradite Garnet. I am not holding my breath yet but it looks exciting
Lou
Hello again I did some further test using my gem eye meter and tested three stones the garnet a zir on and the yellow stone. Yellow stones first zircon next then garnet.
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Well just received my Presidium RI tester and was eager to test my sparkly yellow gemstone. Am I rich?.
No the refractive index read 2.17 Cubic Zirconium oh well still a pretty stone.
Thanks for all your input.
Lou
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Lou,
It seems that you have found an answer on the stone. It definitely has a few interesting measurements to its name nowā¦ 
I have some questions/comments on the instruments you have, if you donāt mind talking about them here.
Spectrometer:
- What spectrometer are you using? You have some interesting spectra on that stone.
- Have you done any tests on other stones to characterize its output? (Like the Garnet and Zircon used with the Gem-Eye)
The Gem-Eye tester:
The instrument uses thermal conductivity. Using it on stones in direct sunlight will affect its measurement. What is the blue putty material? That could also affect the measurement, by generating additional thermal mass especially in direct sunlight.
Admittedly, it did make a handy āstone holderā, thoughā¦
Cheers!
-Troy
Hi thanks for your reply. I like testing different spectrometers first is the thunder optics (quite inexpensive) used with spectragryph software second gospectro which attaches to a smart phone and linksquare which again is used with a smart phone. I am hoping to purchase a Raman spec sometime if I get a buy on a used handheld unit. The gem-eye works well in a cool room and when properly calibrated, I always test known gems first but most important a cool environment, sun not too important. The blue tack material is the material used in watchmaking or the stuff they sell for mounting pictures on the wall, never found it to be themally conductive. Hope that answers any questions.
Lou
Further to your questions I run spectra on known gem stones and then compare them to the unknown if the spectra superimpose then I am fairly certain that they may match. Color difference may show a slight change in specta. I am looking at Raman spectrometers used for drug testing and explosive testing at borders or by fire department etc. Spectra produced are the gold standard and very reproducible.
Lou,
Thanks for the quick response! I thought the blue stuff might be rodico but was thrown off by the deep blue colorā¦ I have only used/seen the sea-green type from Bergeon.
I was curious about the spectrometer types, so thank you! I have been searching for and looking at several types.
I totally agree, a Raman is in my bucket list, too. Although, I donāt think I have come across a hand-held modelā¦ seems more of a desktop item as they are bulky to feed the power-hungry laser module.
If you have seen any modelsā¦ would be interested in looking aroundā¦ I have access to several test equipment vendors.
Troy
Hi Troy I am interested in the First defender Raman handheld it is sometimes very cheap other times 4 or 5 k. You can download lots of gem spectra to it.
Lou,
Thank you! Guess, I had been living behind a curtain of assumptionā¦ 
There is a whole world of hand-held Raman spectrometers, that I was completely oblivious about. Definitely a need for these units in multiple industries and it seems a few folks heard the call and are now grinning all the way to the bank!
Something you mentioned sparked a questionā¦ do you have access to a database of spectra for gem material? You have your two spectrometer systems, so I was wondering if you use a particular database for reference.
This is the only public repository of spectra that I have found so far. I know others exist and some are āyou must join the clubā to access (i.e. you must buy our instrument) ā¦ so I am looking around for other databasesā¦
Unless our esteemed moderator @psanchez says this is already a thing, this is something we should compile for our IGS communityā¦
Cheers!
Yes that is the main database but som universities are doing research on gems with handheld Raman. Would be great to have a spectral database on our site.