almost every sapphire has been already heat treated to improve color and clarity prior to market. they can be heated to 3000 degrees F…without damage but the process is to slowly increase, then decrease the temperature… the crystal structure is trigonal, with a slightly distorted hexagonal closest packing which makes it extremely resistant to pressure cracking… natural can withstand 4 Megapascals per square meter.or 580 psi…synthetic up to 8 megapascals… however, thermal shock generates far higher pressures… if you must heat, preheat at a lower temperature first with a low temperature, low flow reducing flame, and don’t concentrate the heat… makes small passes, then increase to the needed temperature… never quench… let it cool down slowly…flaws in a cheap stone which are internal cracks won’t tolerate the process… the color change that some people have mentioned previously should not happen. heat treating of clear stones in an oxygen rich environment will give it a yellow color. Once the color is set, it’s resistant to further heating…most natural stones are heat treated to dissociate the rutile (titanium oxide) silk in them which gives the stone a cloudiness…heat treated stones can be still distinguished by residual rutile silk “ghosts” where iron is not dissolved… heat treatment to improve the appearance of sapphires is such a common practice that it’s considered legitimate now but diffusion treatment is controversial and fraudulent if passed off as natural… beryllium is added to create a blue color…prolonged heating makes the beryllium penetrate deeper. Diffusion treated stones cannot be distinguished from untreated by the eye or even under magnification… beryllium is detected non destructively by x ray fluorescence…which requires expensive and specialized equipment that only university geochemical labs and the GIA testing centers have…
exellent and very tecnical. thanks
someone else mention gas bubbles. microscopic bubble inclusions contain the residual fluids that created the stone… they vary in composition by how the stone was created in nature…sapphires are formed in high aluminum high grade metamorphic marbles, others from pegmatites, and other yet from peraluminous low silica igneous rocks (lamproites, lamprophyres)…the first is mostly from Myanmar and the last are the Yogo Gulch and Montana sapphires… the bubble contains at least two phases, liquid and gas, and other three, with a solid mineral phase occurring as a microscopic grain…these inclusions diminish the value of a gemstone but are of extreme scientific interest…they are also under a lot of pressure, since they formed within the stone at the high pressure and temperature that created the stone in the first place… heat treating any gemstone with a bubble inclusion risks cracking it since it’s being heating at atmospheric pressure and not the confining pressure that the stone was created at naturally. The best example of a ultra high pressure inclusion was the discovery of “davemaoite” in a blue diamond, discovered in a mine in Botswana, in 2021, that came from deeper than 400 km depth…Dave Mao, a Chinese American, is an experimental geophysicist and petrologist who was the director of the Carnegie Institute of Geophysics for over 30 years…and who was one of the instrumental people who worked out the high pressure-temperature thermodynamics of mineral phase changes deep within the earth’s mantle (660km and deeper), using a diamond anvil cell, wherein a mineral sample in microscopic amounts can be compressed to extremely high pressures and laser heated to recreated deep mantle conditions… at that depth, the pressure is sufficient to change calcium silicate into a cubic structure (perovskite structure) … the structure of calcium perovskite was only theoretical until that discovery and the structure was determined by synchrotron x ray diffraction… I know that this comment is a bit off the practical track, but there’s a lot more to gemmology than most gemmologists are trained in…The GIA has a PhD program in geochemistry…
i love it .
so what can tellme about the type 2 b diamonds like the blue hope diamond with its unique amount of borom in the diamond structure
I am not sure how boron gets into natural diamonds. Kimberlites and allied rocks, including igneous carbonate (carbonatites) lamproites and lamprophyres, do have a unique geochemistry…some incompatible light elements like nitrogen, boron, and LILE (large ion lithophile elements) are concentrated in them…along with light lanthanides (LREEs) light rare earths … the ultimate origin of these elements are recycled oceanic crust, taken down by subduction to the 660km layer and earlier in the earth’s history to just above the core/mantle boundary (DD’ layer)… recycled oceanic crust is also a carbon reservoir… Boron does make them blue colored since the boron atoms substitute for carbon… because boron is trivalent, it creates an electron hole (p-type semiconductor)… that allows for the absorption for red and yellow end spectrum visible light… Nitrogen atoms make a diamond a resistor because they can become quadrivalent. Color centers in different gems remain controversial. Colored gems contain transition elements, whose valence energy levels are crowded together… crystal field splitting spreads the energy levels out, favoring some over the others, that allows for the absorption of some of the visible spectrum selectively via specific energy level quanta… but how it actually works is still beyond me… it requires quantum mechanics to understand…and it’s only one theory of color centers. Green diamonds have natural radiation induced dislocations in the crystal structure… they are more random dislocations rather than natural growth ones like screw and slip dislocations…one of the biggest challenges facing the GIA is how to determine natural green from irradiated diamonds… so far they haven’t found a method, but are working on it very hard… I went to Honolulu for the annual Goldschmidt geochemical society meeting, which is the conjoint annual meeting of the European and American geochemical societies… and there were several scientific sessions presented by GIA researchers… since most gems are sold in mixed lots, no one knows what mines they came from nor what country… The GIA was able to pinpoint the locality of many colored gems non destructively by analyzing thier trace element profiles… using techniques like X ray fluorescence.and spectroscopy…in other cases, they were able to take a microscopic sample and run it thru an ultrasensitive mass spectrometer that was capable of counting individual atoms and sorting them out by atomic weight…thus getting isotope ratios…of both major and trace elements. Diamonds are far more intractable to non destructive analysis or any analysis for that matter…fake green diamonds are so far impossible to tell from the real… synthetic diamonds have identical crystal structures and can’t be differentiated from real, except for being too “perfect”… the makers of synthetics have learned to introduce flaws and also nitrogen, and other colorants into thier products so the potential for fraud is enormous…the Chinese were caught inscribing De Beers on the girdle of synthetic diamonds… the only way to know that one is genuine is from the mine to the retail supply chain… which is why De Beers which controls 40% of diamond market goes thru all of it’s pains to ensure that the real product is sold as such… The Australians were once competitors, threatening to oversupply the market, but they cut a deal with De Beers and have 20% of the market… thier operations are mine to retail certification also… what the rest of the world does, including Russian, Brazilian and West African diamonds are is anybody’s guess… That’s why I’ve never bought diamonds and still won’t…
please don’t quote me on any of this… I am not a professional geochemist… I started out as a rockhound as kid, and was even able to memorize the stoichiometric formulae and crystal classes of common minerals… but finding pretty rocks was too hard…I didn’t count bought specimens as genuine, only the ones I collected… and I do have a museum piece of copper petrified log from New Mexico… but I found that how mineral deposits formed were more interesting and that drab gray and brown igneous rocks were able to tell you thier origins and the history of the earth from it’s inception in the solar nebula to the present by isotope and trace element systematics…all of this is PhD stuff… and I am mostly self taught in traditional isotope systematics…It’s still my hobby, not a profession…
PS: re geochemistry as a hobby… I also did jewelry as a hobby and worked with mixed metals… From what I had learned studying rock phases as they varied with composition, pressure and temperature, it wa easy to apply these principles to alloys and look up thier phase diagrams…and different melting points varying with composition… that allowed me to make my own solders… and 18K gold… and gemstones, mostly semiprecious… perforce I had to study gemology which is just applied mineralogy.
but that was easy… I already knew mineralogy. Now that I am partially retired, I;m looking forward for full retirement. I am writing two scientific papers and will call it quits for my current career in the medical field… time to get a degree in geology next and study it at an advanced level which is geochemistry…but all of this is so useful to gemmology that I feel that I should contribute some science to the discussion…I’m glad that at least one person is not being overwhelmed by my didacticism, for which I apologize… all of the topics under discussion in this community are both simple and very complex. It helps to have the entire worlds’ knowledge at your fingertips, literally via the internet…anyone can look things up on any subject …
amazing
abrielr682140: Yes it really is quite how amazing… drab old rocks can tell you so much!!!.. everything from the primordial earth to the present. How it’s constituents have been recycled (an estimated 6X for the mantle)… they tell you about thier age, what thier original material was made of, and how it was altered and changed by the 1800+ miles as it journeyed to the surface…and that only counts the chemistry in them… seismology has advanced to seismic tomography, where earthquakes small and big are being used like a CT scan to make a picture of the inside of the earth and under the continents and seas… but despite the grand picture that is being painted, there is immediate relevance also to the gems we buy… fraud has become so sophisticated that it takes very expensive technology to detect…The GIA’s mission is to bring order to the market by not only rooting out fraud but to source gems so we know what we are buying…I was gratified that there were three scientific sessions of 45 minutes each dedicated to examining diamonds, sapphires and emeralds… the most expensive ones on the market… and by sapphires, I also mean rubies which are also corundum gemstones, …Although the work presented was research, it is already being put into practice. But the cost of analysis is very high…some of the technology is available only at national labs, where time on the machines are doled out and charged for. The cost of a high tech analytic machine is on the same order of a high resolution MRI machine and costs the same - over 100K to maintain per year, excluding full time skilled technicians who have to be paid well… I calculated that to get a complete analysis on a single rock would cost about $6000… to have an adequate sampling, you need to analyze at least 20 rocks… that would cost 120K… unlike MRI machines that make money for the hospital, there is no money to be made analyzing rocks as pure science…only big mining companies and oil companies have the money to contract out… and thier purposes are limited. national science foundation grants are lacking in funds and universities, even the large state institutions don’t have much money to do that kind of work…Some of the difficult problems that I have tried to wrap my head around and failed to understand, I learned, from more recent papers that the older models were not capable of explaining everything correctly and controversy and unknowns are the normal order of things…and that was why I couldn’t understand things to my satisfaction either… always more research, more research and no money.
exellent information i could tell that you are ver knowledgeable about the subject
I am open to any questions that people may have about gemstones. But I am not a real expert in the field and would welcome others’ comments also. When buying diamonds that are high quality, large and cost more than 20K, the best should come with a GIA certificate of authenticity…it’s the only safeguard against fraud.
thanks . its always good to help
I am happy to share what I know with anyone interested. I would like to have others share also. The field of gemology has become very complicated. The average appraiser and 10X loupe magnification have become antiquated in an era of rampant high tech fraud. the 10X loupe is the standard, and there are may that are complaining that it is now completely inadequate. Buying online thru Amazon or any myriad gem sellers is more dangerous than ever. The stones sold online for cheap are very poor quality now… I bought some of mine online decades ago… more than I could set… the quality is outstanding compared to what is available now at reasonable prices, and prices have increased 10 fold…Since I am no longer buying gemstones, I really don’t know what the current market prices are except high… I visited Tiffany’s just to look and they were surprised that I wasn’t shocked by the very high prices…a 2 ct intense blue sapphire was on sale for 37K… I shrugged it off, not surprised…I used to freak out retail sellers by examining a stone using a physician’s ophthalmoscope… there’s a series of high quality lenses that go up to 40X magnification… by flipping thru the lenses, you can change the focal length and look at the interior of the stones layer by layer…but I must say that I am NOT qualified to evaluate gems. I can answer questions that are scientifically relevant, and answer questions about inclusions which are a window into how gems were formed… but NOT the gem market itself.
I have much more expertise in colored stones than diamonds.
I once questioned a boss about a stone. Was told not a problem it’s a sapphire. I set about and repaired only to have it lose all of its colour.
Yes it was a sapphire but it was a Ceylon sapphire which ended up costing a fair bit to replace.
And never quench anything with a stone even if a little warm unless your pickle is the same temp.
As a GIA trained gemologist (1996) I would take issue with a lot of what you say. I just finished reading an article about advanced equipment to ID lab created diamonds. Some of these instruments are affordable for the retail jeweler, but the more sophisticated ones, no. Sometimes the best you can do is, yeah, this one is OK, and oh, gotta send that one out for more testing. So, yes, as far as diamonds are concerned, the loupe and microscope may not always be all you need. However, when it comes to other stones, there are few that a really good gemologist cannot ID with standard instruments. Beryllium treated sapphired do have their telltale characteristics visible under the microscope and there is an easily found GIA article on line that pictures them and describes them. It is true that some lab created amethyst is indistinguishable from natural that has no inclusions (another case where inclusions in natural might actually be preferred) except with expensive lab instruments…but this separation is more or less meaningless given the cheapness of either natural or lab created quartz. A few years ago there was a scandal when red andesine was “discovered” in China…I think it was in time for the Olympics. Then a US gemologist looked closely at the material under a microscope and saw evidence of brown gunk in cracks and diffusion treatment visible as color in the skin of the stone under immersion and magnification. I think it was Robt. James who blew the whistle…the point is that the info was right there for anyone who looked and I always regretted that it was Mr. James who got to it before me. It was right there for all to see, you just had to have the knowledge and the curiosity to look. Much of gemology is like that. You might need a GIA report to prove heat treatment of sapphire, but anybody who is good at microscopy can separate synthetic from natural. And so on. So you should not be claiming that gemology is now completely the province of the big labs, because there is a lot you can determine with a loupe and a few other tools which cost under $500…the late Dr. Wm. Hanneman was fond of saying that the more gemology you knew, the fewer instruments you needed. Indeed, he and Alan Hodgkinson developed Visual Optics, by which you could identify most faceted stones with no instruments. It isn’t taught much, but it’s real! -royjohn
thanks for your input. It’s good to know that a well trained GIA certified gemologist can distinguish treated stones and fakes from real natural, and it’s also good to know that sometimes, that is not possible without referral to a GIA gem lab. I am not a professional gemologist and don’t have the training and more importantly, the years of experience that it takes.
My point is more about the geochemistry and how good fraudsters are getting at replicating natural stones… we have to expect they will continue to improve thier techniques, making it more and more difficult. The biggest problem lies with green irradiated diamonds. some the lectures I attended at the Goldschmidt meeting was presented by PhD GIA geohemists and postdocs…they were sounding an alarm about how difficult to impossible it was becoming distinguish natural from real as fraudulent uses of high technology techniques advances in step with the development of analytic technology…the current techniques being used to improve color and clarity, and to replicate natural stones for the most part are not sophisticated enough to fool a good microscopist…cheaply produced replicas such as the red andesine be easy to spot, but those techniques are evolving rapidly for high cost gemstones… they also stated that the mission of the GIA was to bring order to the gem market by finding nondestructive techniques to trace the source of stones to thier localities, as well as sounding the alarm when something appears on the market that is not genuine nor a “real” gemstone, even if semiprecious…the GIA imprimatur of a certificate of authenticity still remains the gold standard. Without the GIA, the market would indeed be in chaos…but it’s still caveat emptor…especially for online sales. The Chinese seem to be the worst offenders but they are also very good at science now…they have the most recent up to date technology as we have when it comes to geochemistry, with many papers being presented by Chinese authors.
So far as advanced technology is concerned, using an ultrasensitive mass spectrometer is unnecessary almost all of the time, but is being used actively for research by GIA PhD’s… X ray fluorescence machines are far cheaper, thought not cheap, and offers a nondestructive method for obtaining trace element profiles. Trace element profiles are invaluable in any mineral and rock analysis for in depth study… isotope systematics add an entirely new dimension and is even more important, but that involves mass spect.
Flaws and inclusions are actually more interesting to me than the gemstone itself. changing crystallographic orientation as layers are built up on layer by natural processes give us information on mineral paragenesis and whole rock petrogenesis…So are the trace element profiles and isotope systematics…
addendum: it’s only a matter of time when illicit use of high technology will fall into the hands of Chinese fraudsters… but as you have so nicely stated, the use of optical tomography at high magnification does not require expensive equipment, and still fortunately, is a very good way of looking at both natural and treated stones… my own personal experience with this technique is to use a medical ophthalmoscope which does show a lot more than a 10X loupe… but without years of experience and formal training I don’t always recognize and identify what I see. I quit making hobby jewelry many years ago and still have a hoard of unset stones, so I’ve been out of the gem market that long also…and have no need to re enter it… my primary interest is the whole deep earth and not gems…the story of how the earth evolved from it’s inception to the present is written in the chemistry of igneous rocks… the formation of gem and precious metal deposits by fluids and volatiles under high pressure and temperature conditions interest me more than the gems and metals themselves… the reason for my long winded exposition is because there are upcoming dangers and that the GIA will remain the watchdog over the landscape of gemology.
This is a very ‘popular science-level’ article, but well written and interesting.
It is hard to imagine that diamonds could come to the surface from 400 miles below.
Neil A