Anyone know what inclusions in Rhodolite should look like? I bought some small stones (7X5 ovals, about 1ct each) for about $2 each. (eBay, Thai seller.) They make nice earrings. I thought I should do some due diligence before possibly selling them to anyone though.
The RIs are in the 1.77 range, consistent with garnet.
On the polariscope about a third of them are clearly singly refractive, about a third have a small amount of blinking and about a third have quite a bit. The article here in the polariscope class gives instructions to detect ADR and it seems to indicate that it is, but I don’t have much experience.
Under the scope I am seeing some bubbles, sometimes arranged on a plane like a veil. I will try to attach some pics. I was wondering if the bubbles indicate a synthetic?
There are three different stones in the pics. The first two pics are one stone, the next one is a second stone, and the bottom two are the third. The bottom two look like natural rutile or similar needles but the first one is the one that worries me.
hi
i am replying to your post in that you will reply to my post (Opinions wanted).
Have you looked at the mini courses ISG offers, courses name Garnet Specialist Mini Course
you might find a lot of good information.
Happy reading.
I’m working through the PG course now so I haven’t looked at any of the mini courses yet. Other information here would indicate the rutile silk is natural but bubbles are not. Maybe I have a mix of stones?
While your due diligence is certainly commendable, it is all for just a $2 gemstone.(?) These garnets are quite common. Keep making those nice earrings!
That’s right more experience becomes more knowledge. The gemstone world has a long list, eg diamonds and pearls are in a class of there own. knowledge and skills takes time, over a period.
These stones look to be natural. I don’t think there are any synthetic versions of the coloured garnet varieties probably due to their abundance and low value.
These stones seem to have prominent crystal inclusions some with staining (confirming natural). There is also evidence of needle inclusions (rutile) which intersect at 70 & 110 degrees. Rhodolite being a blend of Pyrope and Almandine garnet varieties, the needles are derived from the almandine influence.
To absolutely determine their variety you would want to determine the following:
Single refracting or double refracting - S/R therefore will also be monochroic.
Refractive Index - 1.750-1.770
Specific Gravity - approx 3.90
There should also be an identifiable absorption spectra.
Thanks. I agree, there isn’t much incentive to fake them at $2 a ct ! But the first stone pic made me a bit nervous. The RI’s are good, and the polariscope tests looked mostly good too with a little ADR possible. Haven’t gone to the trouble of calculating SG.
Your RI of 1.77 isn’t right for any synthetic but possibly corundum, and that should be doubly refractive with one index below 1.76. Syn spinel at 1.72 is too low. If I had the stones in hand, I would look at a light source through them and easily tell whether they were singly or doubly refractive by Hodgekinson’s visual optics, as the “rainbows” in the stone would be single and not in pairs like in tourmaline and peridot, for example. But if you only see one RI, then they are singly refractive and what you’re seeing in the polariscope is ADR. So first, there isn’t any synthetic in this RI. Second, they are bellied and cut for weight, which synthetics often aren’t because they are so cheap. Third, the inclusions in the first picture are elongated and the microscopic gas bubbles in flame fusion corundum are much smaller and round, as are the larger round bubbles in glass. Another thing is that there are the five or so elongated inclusions on the right side of the photo, but there are also a swatch of inclusions of irregular shape on the other side. You’d need more magnification to resolve what these are, but they look like they could be crystals of some kind. The elongated bubbles might be fluid inclusions or three phase inclusions. The rutile needles in the other stones are characteristic of garnet, too. I think you can safely call them garnets. Your example points out why it is so useful to have access (on line or elsewhere) to a good library of microscope inclusion photos, as often, if he RI is one for both a synthetic and natural stone, this is the only sure way to differentiate natural from synthetic. Flame fusion is usually easy, but some of the other synthetics not so much. -royjohn
It’s hard to see from the pic, but are those bubbles inside the stone, or are they small notches or divots on the surface of the stone?
The reason I ask is that many ancient gemstones have such notches/divots, and a couple things suggest those stones were worked a long time ago (when considered together): the source location (especially if these are from the Khmer/highland regions of Thailand, the slight variation of hue in the band of faceting around the base of the stone, and the faceting style. Of course, it’s hard to tell without looking at them closely and for some time, and old stones are regularly treated or further worked in modern times, but if ancient, these features would be normal.
If you’d like to see other examples please PM me and I can share several of different types of stones all of which exhibit similar features.
your knowledge of optics is impressive!.. wonder whether there’s much synthetic gem garnets on the market… natural is abundant and fairly cheap… mostly know that synthetics like YAG are used mostly for lasers and electronic applications…dopants will create all colors of the rainbow. critical angle of refraction for YAG is 33 degrees, natural depending on type between 33 and 35 degrees.
Natural garnet can have bubble inclusions but due to the pressure and temperature of formation these are not common…(green schist facies, medium grade)…sometimes found in cavities along with topaz and cristobalite/trydimite and exceptionally with beryllium (red beryl)…in S type (tin) rhyolites as very small crystals (low pressure medium temperature)… synthetics tend to have more bubbles…
I don’t know whether there is a physical or optical way to distinquish doped YAG from natural…absorption spectrography shows strong lines from dopants but no markers for Y, since pure YAG is colorless…if I am not mistaken, XRF should show yttrium… Yttrium can occur in natural garnet, especially Mn containing species up to 2%, but never is the major element component of natural… If present as a dominant element, the garnet has to be synthetic- YAG
In part, I think I have answered by own question… thinking of optical spectroscopy, manganese would color YAG red…optical spectrogram would show sharp lines rather than broad bands at 350 and 400nm for Mn+4 and Mn+2 when coupled with a negative oxygen ion or negative void…
