Geographical Origin of Gemstones.
Gemologists have been facing this long-standing problem of deducing the geographic origin of gemstones. Researchers have devised several devices to simplify this challenge. But gemstone mines keep multiplying around the globe. This proliferation bogs down gemologists trying to ascertain the geographic origin of gemstones. The puzzle has become particularly pronounced during the last ten years.
There are many reasons. The foremost amongst them is its financial implication. The value of a gemstone depends on many factors. The Four Cs, namely cut, clarity, carat weight, and color are well known. However, in the case of colored gemstones, one more critical factor comes into play. It is the area where the stone came out of the ground.
It is the story behind the stone. For example, suppose a buyer is out to buy a ruby in the market. There will be different stories behind the various stones available.
Story A: A miner is wading and digging gem gravel in a river in Cambodia for days together by hand. He suddenly stumbles upon this gorgeous gem-quality ruby. His eyes light up with the excitement of his discovery. And you are now holding this cut and polished stone in your hand.
Story B: A scientist in a lab coat pulls out a lab-created ruby from the furnace with a pair of tongs. He, too, is excited about the success of his endeavor.
There is no good or bad, right or wrong between story ‘A’ and story ‘B’. It is just that the market attaches more value to the natural ruby depicted in the story ‘A.’ Therefore, that ruby is more valuable.
Story C: A buyer comes across a natural ruby from Mozambique. You should note that Mozambique is a relatively recent source of Rubies with no great legends attached.
Story D: A buyer comes across a ruby from Mogok mines in Burma. Mogok mine in Burma has been producing Rubies since antiquity. It has been presenting the red gemstone to royalty and noblemen. Its history is replete with legends and lore.
Again there is no right or wrong good and evil between ‘C’ and ‘D.’ Nevertheless, gem lovers find the Burmese Mogok ruby much more appealing. It is what the mind perceives. And perception is everything. Consequently, the Burmese ruby is much more valuable.
Another notable example is the blue Sapphire from Kashmir. This stone carries immense prestige and value.
Thus, we see that determination of the Geographical Origin of Gemstones is essential as it directly impacts the value of a gemstone.
Besides, buyers are environmentally conscious. They want to know whether the mines yielding the stone indulge in eco-friendly and sustainable practices. They want to know the ethics behind the trade and whether it involves child labor. The government might want to see the source to prevent money-laundering and other illegal activities in the guise of the gem trade.
As such, the determination of the geographical origin of gemstones plays a vital role in the world of the gem trade.
Most people in the industry do not adequately understand the realm of geographic origin. Only experts with many years of experience and access to the right technological tools grasp the intricacies of origin determination. Yet, pseudo-experts with half-baked knowledge offer this service and issue certificates. And unscrupulous elements use these certificates unethically to market gemstones.
Plethora of Sources
In the 1950s, Sri Lanka too started supplying rubies. These rubies shared some similarities with Burmese ones. Yet, they were disparate enough to be differentiated without difficulty.
Kashmir, Burma, Colombia, and Russia were the primary suppliers of Sapphires. Ceylon [present day Sri Lanka] was another major player. Finally, Australia and Thailand contributed darker basaltic sapphires.
Since 2017, sapphires from the Ambatondrazaka region in Madagascar have entered the market. Prima facie, these sapphires resemble those from Kashmir. However, their inclusion profile is different. They do not carry the characteristic inclusions of Kashmir sapphires. The pargasite needles, short-prismatic Tourmaline, and corroded long-prismatic zircon inclusions are all hallmarks of Kashmir sapphires. And they are absent here.
The Ambatondrazaka rough comprises a range of stones with low iron content and milky aspect similar to Ilakaka and Sri Lanka stones. Some of them exhibit higher iron content with a silky feature akin to the blue sapphires from Mogok. Metamorphic blue sapphires pose the biggest challenge for origin determination.
GIA in Bangkok recently examined a batch of rough corundum originating out of Badakhshan. These specimens showed dust-like or ladder-like inclusions matching those seen in sapphires from Kashmir. Raman spectroscopy established Tourmaline was one of the inclusions here.
Ethiopia is a surprising entrant as a source of precious colored stones. The Axum town in this region is a source of blue Sapphires. The Shakiso township in the Southern part produces Emeralds. The area also sires Opals. Field gemology teams had to promptly visit these areas to collect sample stones because of the surprise element of the finds.
After a long hiatus, the Mariinsky priests emerald mine in Russia, and the Russian Urals became significant emerald sources again. Trace element profiles of these Russian emeralds are similar to those of Zambian emeralds. And regions in the vicinity of these emerald mines are sources of demantoid garnets.
An expert gemologist can identify the country of origin of many of the stones. But in some instances, it becomes impossible. For example, an extreme overlap of properties renders the task undoable. It is also possible that the property of an unknown stone will not match anything in the lab’s database. In such cases, determination of the Geographical Origin of Gemstones becomes impossible.
How is Geographical Origin of Gemstones Determined?
It is a science, but not an exact science. Therefore, gemologists use many different methods to deduce the origin.
800 Years Ago:
In the days of yore, there were very few sources of quality gemstones. Consider the era of around 800 years back. If a gemologist came across a supreme quality ruby gemstone, he could immediately surmise that it was from the Mogak mine in Burma. The region’s name might have been different at the time, but he could pinpoint the origin since there was only one source of quality ruby.
300 Years Ago:
As we move ahead in time, say, now we are three hundred years in the past. One more large source of ruby has sprung up. It is the present-day border between Cambodia and Thailand in Pilon. This region produced high-quality gemstone, albeit of darker color, in substantial quantities.
100 Years Ago: Arrival of the Gemological Microscope:
A gemologist now had to contend with two sources of supply, but some 100 years back, technology came to his aid. It was the gemological microscope. The gemologist could peer into the stone and identify the inclusions. For example, the inclusions in the Mogak ruby were iridescent rutile silk. He would have seen nested straw and needle-like silk.
On the other hand, Thai ruby does not display rutile-silk patterns. Here, the gemologist would see solid inclusions in hill-like patterns of heat-shattered minerals. The two deposits were distinct. Hence, differentiation was not difficult.
40 Years Ago: Arrival of the XRF or x-ray Fluorescence Instrument:
Technology kept evolving, and the XRF or x-ray fluorescence instrument arrived around 40 years back. This tool makes trace element measurements inside various colored gemstones. At that time, the gemologist would put the ruby inside this machine to measure its iron content. Iron proportion higher than 700 parts per million atomic meant a Thai Ruby. Iron composition less than 300 parts per million atomic denoted a Mogok ruby.
But the difficulty got compounded by this time. New sources of ruby started mushrooming all over the place. So, you now had many more regions to identify as the geographic origin of the gemstone.
There was one more deposit in Burma. This time at Monceau. You had an excavation in the Luc Yen area of Vietnam. But the most significant phenomenon of the 20th century in the gemstone mining world was the proliferation of discoveries in East Africa.
Prospectors discovered many new deposits of sapphires, rubies, emeralds, garnets, opals, and other gemstones. The reserves were scattered from Kenya in the North to Madagascar in the South, including Mozambique.
Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS).
All at once, you now had to reckon with several new possibilities for the stone whose origin you were attempting to ascertain. But technology also is more advanced now. It is known as laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). This method diagnoses the trace elements in colored gemstones with high precision and accuracy. Moreover, it enables the comparison of more sets of data.
The laser ablation device focalizes a laser beam on the gemstone girdle. As a consequence, an infinitesimally small amount of the gemstone gets extracted. A plasma consigns this iota of the gem into a mass spectrometer. The spectrometer measures the trace element chemistry up to the atomic level.
An analyst plots the results onto a graph. A highly skilled and experienced gemologist then compares the chart with an existing diagram from a stone with a known source of origin. It is very technical and full of scientific jargon. Suffice it to say that the geographic origin of the unknown stone under study is determined by comparing it with the LA-ICP-MS graph of stone with a known source of origin. The latter exists in the archives of the gemological laboratory.
Then again, multiple sources of origin create overlapping LA-ICP-MS graphs. It is here that the knowledge and skill of the gemologist come into play. He makes use of this selective plotting method. It selectively filters out dissimilar reference data to narrow down the probabilities.
Scrutiny of the stone inclusions is used in conjunction with the LA-ICP-MS graph to resolve dilemmas if any.
Machine learning is also increasingly used for the intelligent crunching of data and achieving accuracy and confidence in results.
This brings us to the next pertinent question.
How is the reference data existing in the archives of the gemological laboratory collected?
We consider Doctor Gubelin as the founding father of this field. He studied inclusions with a lot of passion. GIA’s Mr. J.I. Koivula joined him later. Together, they undertook the most exhaustive study of gemstone inclusions. They recorded their findings and observations in three stupendous volumes. These publishing illustrated the inclusions you find in a gemstone of a particular geographic origin. They also recorded the pattern of inclusions in heat-treated stones. They even included the form of inclusions observable in lab-grown gems and imitations. Their work laid the foundation of origin determination. Experts concur that the three books are still the bibles of Geographical Origin of Gemstones. They are the go-to place for anyone trying to ascertain origins.
How are the reference stones for determining Geographic Origin collected in a Gemological Laboratory archived database?
Reputed labs like the Gemological Institute of America (GIA) depute their gemologists in the field for collecting these reference stones. And the team of gemologists and other experts lead expeditions to known sources of gemstones around the globe.
At times, gemologists can go into the mines and pull out the gemstone with their own hands. They take all the possible information of the stone on record. The name of the mine and miner, mine location, GPS coordinates, etc., are meticulously recorded and preserved alongside the gemstone. The pedigree of such a stone is impeccable. Such a stone becomes the most reliable material in the archived database. Subsequently, gemologists compare the data from this stone to establish the origin of an unknown stone that comes into the lab.
However, it is not always possible to find a reference stone in such a reliable manner as one cannot always acquire the stone straight from the mine. A gemologist may excavate for days and not find a gem.
At other times, the gemologist might not be allowed into the mine. It happens because miners are understandably secretive about their source.
Sometimes, the gemologist might view the miners taking out the stone though he has not done this himself. Even this stone is quite reliable. At other times, the gemologist might have procured the stone from a market near the mine. This stone is much less reliable as a reference stone. But it is nevertheless retained for want of a more reliable stone. Often, stones are from the international market that might even be in a country different from that of the purported origin of the gemstone. Such a stone is the least reliable reference gemstone.
Accordingly, gemological labs classify the stones from A-type samples, which are most reliable, to F-type, the least reliable.
Reputed labs collect thousands of such gemstones weighing millions of carats for years or even decades.
Type Of Work Done in the Lab:
The laboratory then starts its research work:
1. Gemologists polish wafer-thin parallel plates into the stone.
2. They scrutinize the inclusions under a microscope.
3. They record the type and patterns of inclusions for posterity.
Experienced gemologists subject the stone to all the aforesaid technologies like Raman spectroscopy, UV-Vis spectroscopy, FTIR spectroscopy, and the laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS).
The researchers meticulously record their observations in the annals of the gemological lab. They construct an extensive database over the years in this manner. Eventually, the lab uses this information for origin services offered by its office.
A gemologist preparing an origin report of an unidentified stone accesses all this data. He gets into this database and compares the gemstone on hand with the data from stones of known reliable provenance collected in the field. He can thus make a correct identification and issue the certificate for Geographical Origin. An ancillary benefit of this collection is that the same set of stones also aids in heat treatment studies on gemstones.
Fast advancing technology might make it better possible to determine the geographical origin of gemstones in the future than what it is now.
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