(re-posted since I messed up the last post lol)
I obtained this 2.59 carat cut specimen being told its a color changing garnet from Africa. I am aware that there is color changing garnet material from tanzania and I was wondering if this could possibly be of that material. I am an amateur in high-school that has a interest in gemology but I freaking love gemology so much and I love learning about the scientific aspects of gems along with their value and had to self teach myself a lot of information. Im fully aware that I have nowhere near the amount of expirence and tools a gem lab would have to make a well educated opinion on what this material can be, but with what I have so far ive been able to bring some bits of data and observations that I believe can help determine a guess or opinion on what this material is. At first glance, it appears to be a gem with vitreus luster with moderate inclusions and one of the first things I decided to checked that would help shorten the list of possibilities was its refractive index (which my refractometer is definitely not professional quality but it does give somewhat close to accurate information but sometimes it will be off by ±0.1) and it seemed to have a RI of approximately 1.775 and be singly refractive in which I determined from the different positions I measured its RI in and with the help of a polarizing filter. Since its singly refractive, the first things that came up in my mind is garnet, spinel, and glass. The RI seemed to be a little high for most spinel im aware of though from the book “gemstones of the world” by Walter Schumann it does say the RI of spinel can reach as high as 1.762 so it could possibly be an option since I need to take into consideration that my refractometer is sometimes slightly inaccurate. And when it came it glass, Im aware that most of the time glass will have a refractive index under 1.7 though certain doped glass especially when used for visual appeal or jewelry purposes like lead glass can have a RI of 1.7 but with what I recorded with my refractometer and it only being inaccurate usually by ±0.1 units I dont think this could be lead glass but I have read an article here talking about glass that was used to simulate rough garnet and it having a higher than normal RI for most jewelry used glass. Now when it came to garnet, my observations made the most sense as garnets depending on what species, varieties, and mixes can have a RI thats anywhere in the 1.70’s to being over the limit for standard 1.81 max refractometers. Since this material displays color change Id assume it could be a combination of a garnet species since thats usually what most color changing garnets tend to be. Im still not quite sure exactly though what species or variety or mix this could be and wether its a mix in the aluminum pyralspite group or calcium ugrandite group. And as for its color change itself, in person its a yellow chartreuse color in fluorescent light and in indirect sunlight its a chocolate hazel brown while in direct sunlight it becomes a brick red color. On camera it seems to change for fluorescent lighting where it becomes more beige in color and more of that brick red in incandescent light as you can see in the photos. I put it under short wave UV light and it showed no sings of flourescence at all which might possibly be due to iron content I suspect if it is a natural material. I also checked for any pleochroism with a calcite dichroscope and nothing really seemed to come up, I then also used a linear defraction spectroscope and noticed a medium to medium faint absorption band at roughly 455 nm with a medium to medium faint broad absorption from roughly 470-500nm with also a very faint band at around 560nm and then the spectrum started to fade out at around 560-600nm. Im still unfamiliar with absorption spectra so im not too sure what this can be indicative of. And finally I had used a 40x luope to look at its inclusions and noticed that the gem seemed to have a faint treacle similar to that of hessonite. From what I could see, it seemes to have single phase inclusion of some dark material, possibly of some type of mineral. Then there appeared to be small scattering of bubbles which I could not determine what was inside them wether they had liquid or gas or both. The bubbles of course made me think of glass but with the other inclusions inside the matrial I seem to highly doubt that the whole material is glass but if anything the bubbles could be a sign that the material was maby treated by some sort of filling like glass filling. An intresting inclusion I found was what appeared to be mutliple or just 1 parallel tabular growth inside the gem which seemed to possibly be hollow which made me think it could from some type of mineral growth that was traped inside the gem and was later dissolved away. It may have been just 1 inclusion as the reflection of the facets may have made it appear to be multiple but im not too sure if this type of inclusion is common amongst garnets like how hollow parallel tubular inclusions would be common for aquamarine for example. Of course I still yet have all the knowlege, tools and expirence to determine exactly what this material is and if it is natural or not or even if its a natural material that has been treated. But I so far im leaning towards it likley being some sort of natural material wether its treated or not and possiby some type of color changing garnet like I was originally told. I would love though to hear what other people might have to say on what this could possibly be and also if other people have expirence any color changing garnet with similar colors and aspects of this material
(re-posted since I messed up the last post lol)
Deflated Octopus (cool name),
Claiming to have taught yourself, you have an incredible knowledge of gemology and classical equipment.
I believe your instincts are working very well. By chance do you have one of those strong little rare earth magnets? I would be interested to know if you can drag that stone on the counter with it?
I think you are on the right track, but for right now let’s work on a process of elimination.
I do not have any strong earth magnets but that would be an interesting test to do. And yeah of course I dont have a raman spectrometer just chiling in my room but using what Ive got so far and the process of elimination can definitely help so much to determine what something could be. Afterall most gemological identification done in labs just start out with process of elimination, but man once it gets to identifying certain inclusions and treatments I think its so cool that you really have to get intimate with the specific details and science of gems and minerals. So much chemistry and physics haha, and in the future I’ll probably get myself more tools such as a polariscope and a specific gravity kit to really help with that process of elimination. And hopefully I can someday I can afford to get my hands on a gemological microscope.
thank you for the pdf, it was a nice read and really blew my mind all over again with how complicated but also how much of a headache identifying garnets can be. This is why I love garnets since they are just so complex and fascinating and In fact, hopefully I can build myself a similar contraption to use for my garnet collection one day. In the meantime just for fun, I grabbed a normal magnet that I have on my light pen which is used to hold its cap in place and and tried to see if I can pull any gems with it. To my surprise, some gemstones I had were actually attracted to the magnet and I was able to drag some gems across a flat surface using it. Among my garnets, I tested my purple to red rhodolites, mali garnet, spessartites of varying shades of orange, and my suspected color change garnet. All the rhodolites and mali garnet had no reaction, however the only ones that did show a reaction where a select few of my spessartites and my potentially but not confirmed color changing garnet. My spessartites varied in shades of orange with one being more on the deep reddish orange side(which I suspect might have a higher iron content aka almandine content) to some being more on the pure orange side such as with a “fanta” or “mandarin” color(which I suspect is from a higher manganese aka spessartite content). Turns out only the purer orange colored spessartites seem to be dragged by the magnet while the spessartite of a deeper red orange color had pretty much no reaction. All my spessartites are OTL on my refractometer which makes me more keen to believing they are majority spessartite potentially of the spessartite and almandine mix and the pure orange ones then might be more spessartite composed due to higher levels of manganese, which could then be responsible for making the gem over all more paramagnetic than the more reddish spessartites. As for my supposed color change garnet reacting to the magnet, I’m still not sure what composition it could be as I don’t have the equipment to obviously get more adequate data. However, since it does seem to be pulled by a simple magnet I supposed that can hint to certain transitional metals being present that are making the material paramagnetic such as possibly manganese which if confirmed could hint it towards being a variety of color changing pyrope-spessartite but I’m still not sure. Thank you though for that study as it was quite informative but I’m defiantly gonna need to re-read it and expand my knowledge to better understand garnets now haha.
Tanzania is in Africa to start you off. The colors in the change look spot on.
Being a self taught gemologist in high school, you are on the right track. Congratulations! I wish I had kept up with my studies when I was your age and not starting again when I hit my late 50’s. I’ve been cutting turquoise, opal and a few other stones since high school but that is about it.
I know you are on a limited budget right now, so check on auctions and even at your school to see if they have any lid microscopes that they are not using. Sometimes they clean out the labs and just toss some of the older equipment. It still works fine and it can be used for gems till you can afford a better one. You can look on eBay for used equipment also. Be sure that you have a chance to return it if it does not work.
All the best,
Thanks for the complement, as of course im no where near being an actual gemologist but knowing the basics and applying it into this hobby while also being open to learn and acknowledge more information can always help someone get a better understanding into gemology. Even with this supposed “garnet” I still dont have all the right data to confidently make that assumption but with the limited data I’ve been able to collect so far, It can help me with boiling down the options of what this material could possibly be. But man this hobby can be expensive, and even more expensive if I wanna take it seriously but saving for some tools like a specific gravity kit, polariscope with an interference ball and hopefully a good binocular microscope can definitely be something In my reach I can look foward to.
P.S. I was aware of Tanzania being a country inside the continent of Africa😂 just that Africa was the only information I was told about the origin of this “garnet” so I questioned if it could possibly be of Tanzanian origin which some color change garnets are known to have come from.
You can make a SG set up with a good scale, some wire and a cup of water. Just look up the directions on the internet. A polariscope is real simple to make as well. Directions can be found as well. My grandsons wife has just decided to get into gemology also and is on a limited budget. I have just sent her all of my starting equipment. I bought all of my first equipment on eBay at a great price. I kept watching out for the best prices for used. I’m retired and disabled so I was on a limited budget. I was also buying stones to work with. I found some extra stones to start dealing and started making some set pieces and making decent money. I started getting clients and my business went from there as my experience and education went up. My ability to cut and finish opal, turquoise and other stones did help. I am also a silversmith and artist so that was a huge help. I took courses in high school and college. You can find courses in any Jr college after hours and they will let you take them as a high school student. They will let you take them at a cut rate cost being in school already. Your local library has a great resources of gemology books on hand. Fo pick the brains of your local jeweler and possibly get a job in a jewelry store. They love someone with a basic knowledge of stones and some will sponsor you in a GIA education.
All the best in your endeavors,
As far as I can tell, everything seems to be going in the right direction. Though from my experience, I would call this a color-shift champagne to orange.
Ideally, you want to go from florescent to candlelight to get the greatest color change, with fluorescent to incandescent being a close second.
Also, some garnets (as you have discovered) and other stones (like zultanite) have different shifts depending upon the color temperature. (Light temperature is measured in Kelvin).
Here is a quick reference chart of common temperatures:
*1900K (Warm White) Candles and many vintage style LEDs
*2700K (Soft to Warm White) Most common for Incandescent lights
*3000K (Soft White) Halogen Lamps. These were the over head lights that took forever to warm up. Still common in school auditoriums and gymnasiums as well as some older conference rooms.
3500K (Natural White)
4000K (Cool White) Common for CFLs
4200K (Cool White) Common for Florescent tubes
5000K (Daylight) Also called bright white
*Please note, different lighting manufacturers will flip “soft white” with “warm white” on their color charts.
Look for the specific Kelvin rating to be sure. As a rule, LED lighting will have a different balance than their non-LED counterparts. It is the average of the wavelengths that give them the appearance of the non-LED counterparts to the human eye.
Bonus trivia: “Warm” stones look best in warm lights and look muddy in cool lights. “Cool” stones look best in cool lights and grey-ish in warm lights. So if you want to display your stones, lighting matters.
You have been doing great testing on your gemstone. Just sharing here a couple of resources you might find helpful:
A quick reference that I found to help me get an idea of what a gemstone’s RI might be quickly looked up:
I also own the reference Gemstones of the World. Love that book.
I have also just received my copy of Gemstones of East Africa and have been reading it. Love the maps and full color photos of roughs and finished gemstones. The writing is excellent.
GIA.EDU also has a free online gemstone encyclopedia for you to read and use. I hope this helps you in your learning journey!