ok, to address the visual optics stuff: i may be overestimating the ease of picking this up because it does help to have a basic idea of what's going on. first, understand that there's nothing mystical about a spectroscope: all it does is break a beam of light into its component colors (dispersion). this is the same thing that happens with a prism (and, indeed, one type of spectrscope uses an internal prism), and also the same thing that happens when you view a gemstone from certain angles. "fire" in a diamond is nothing but dispersion.
vo uses this effect. in a darkened room with a single pinpoint light source, hold the largest facet (typically the table) as close to your eye as you can without touching it. if you rotate it slightly, you should see an array of tiny spectra. in gems with a low refractive index, you may see rings of spectra; with high ri gems, because the light is bent so much, you will see only one arc of a single ring.
in doubly refractive gems like ruby, each spectra will be doubled--you will see two in a line, not parallel but one after the other, sometimes overlapping slightly in which case they will look somewhat fuzzy.
again, the spectrum you're seeing is pretty much the same thing you would see in a spectroscope. ruby has strong absorptions in the center of the spectrum (this creates the red color), so the spectra you see will appear more like red and blue dots. garnet does not show this effect. its spectra is closer to a typical "rainbow" appearance and looks nothing like the ruby spectra, which is why richard was able to id that gem so easily.
So, now I will go out and get a pen light and try Richard's method. Somehow I feel I will just not get it again, seeing as how badly my untrained eye is missing all these things. But maybe I should just go out and get some rubies for comparison...?
are you looking for these with a microscrope or a loupe? it's a lot tougher to see them with a loupe. also, 95% of the synthetic rubies on the market are flame fusion, because it's the cheapest method, so if it's a synthetic it's almost certainly one of those.
You won't see gas bubbles with a loupe; they're small enough that they'll look like pinpoints at 10x. You might be able to see the curved striae, though. Get yourself a bright flashlight and cover the light with a kleenex. Then look into the stone with the ring on the flashlight, looking directly down into the light. This creates a diffused direct lighting source that can make curved striae easier to see. What you're looking for is a faint, subtle texture much like the lines on an lp record. at 10x it will be tough to pick out, but you might be able to spot it.
well, there are varying degrees of fluorescence. some thai rubies can be so dark that their fluorescence is very weak, weak enough to be missed outside the laboratory. i've seen a few of them like that, and these are, unfortunately, the stones most likely to be mistaken for garnets because of their dark tones.
It looks like a red garnet to me. Another decade or so, such sizes won't be easily available anymore.
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