Among all the colors that exist in nature, the human eye is most susceptible to green. At dusk, when the world around us is plunged into darkness, green objects are the last ones that «lose» color. It is not surprising that for five thousand years the emerald has remained one of the most valuable, attractive and revered colored gemstones in the world, along with ruby and sapphire.
Unlike diamonds, inside which light is refracted and turns into millions of small rainbows, emeralds do not sparkle — they shine. Specialists call this effect “vitreous lustre”. They compare it with still, moist nail polish. For this mineral, the primary feature is color – pure bright saturated green color to be exact. The hue of the stone is determined by the impurities. Chromium and vanadium imparts it to the blueness, and iron, to yellowness. The specimens from the second group can be very beautiful. But because of the yellowish tinge they are less valued in the market.
The benchmark emerald has a bright, pure saturated green color of medium lightness with a possible barely noticeable bluish tint, evenly distributed throughout the volume of the mineral without visible growth lines. It should not be too dark or, on the contrary, too light. In the first case, the beauty of the stone suffers. In the second case, the emerald turns into green beryl, the most valuable member of the family in which it belongs. This has been a source of confusion and dispute for many years. In most cases the “social class” of the mineral depends only on the personal perception of the gemologist.
Emerald formation and extraction
Emerald deposits were formed as a result of orogenesis (mountain folding). This phenomenon occurred more than 4.5 billion years ago. Two plateaus collided, a continental plume formed folds, and very high-temperature water would vent through the faults of rocks to the surface of the earth, which also included chemical elements (in the case of emeralds there was chrome). The liquid broke through the black solid crust of pressed shale and got into the voids of the rock, where beryl crystals grew. All of this led to the birth of emeralds.
Today, these stones are mined either in quarries (mainly in Africa) or in mines (usually in Colombia), with a maximum depth of 150-200 meters. The whole process from raising minerals to the surface of the earth to their washing, sorting and sometimes cutting, occurs within one fenced area. This is because the owner of the field may usually struggle with theft.
Earlier the extracted crystals were transported for further processing to specialized centers. But some of the raw materials disappeared without leaving a trace, settling in the pockets of light-fingered workers. Thus currently the uncut emerald leaves the territory of its extraction only after it is washed, weighed and evaluated. From the whole amount of raw materials found, no more than 15% of all crystals have jewelry quality.
If you compile a scale of values for precious beryl, first place undoubtedly goes to minerals taken from Colombia (especially those mined in Muzo). After the legendary mine of Cleopatra in Egypt and the Habach Valley in Austria, which were exhausted long ago, Colombian emerald deposits are considered the most ancient known ones today. Secondly, these stones have the most rich and beautiful palette of shades.
Second best are minerals from Zambian deposits. These were discovered in the 19th century. Unlike Colombia, African emeralds have a less interesting palette and are estimated to be about 4-5 times cheaper than their competitor. At the same time, some specimens of emeralds from the Afghan source, Panjshir, may cost more than the reference stones from Zambia. Moreover, with the discovery of three new deposits in Africa, experts predict a glut of the market with African stones, which will lead to a drop in prices for them.
The step below is Russia. Specifically, the Malyshev mine in the Urals recently resumed its extraction of precious beryl. They have a yellowish tint, but can be quite beautiful. And, finally, Brazil — from this source a lot of emeralds emerge, but they are all very bright and almost never have high quality.
Among other producer countries, one can also mention Pakistan, India, Iraq and China. As a percentage, reference stones are most commonly sourced in Colombia, but can generally be found in absolutely any deposit. In addition, the high cost of Colombian emeralds, which has increased markedly in recent years, forces jewelers to rely on African raw materials.
Irrespective of the deposit, the vast majority of natural emeralds have inclusions and cracks. They undermine the structural integrity of the stone and make it vulnerable. Even one minor blow can easily destroy the mineral, despite the fact that on the Mohs scale, the emerald gains an impressive 8 points.
In some specimens inclusions are minimal. In others they are located throughout the whole volume. Specialists named them “Jardin” (French for “garden”) comparing internal defects with interweaving branches of trees in an abandoned park. However, the truth remains unchanged — the purer the stone, the less often and, consequently, the more expensive it is.
To visually improve the state of the mineral, as well as give it additional protection against further cracking and dying, it is subjected to oiling. And, some twenty years ago, this procedure made dealers feel fear and mistrust. The final customer simply did not know about it. Nevertheless when the truth surfaced on the retail market, people were disappointed and offended. Because of improper keeping, the oil from the beryls outflowed, which led to sad consequences. It happened because the sellers did not explain that these stones should be kept in a humid condition (or have a small vessel with water next to it). Today, the number of untreated visually clean stones available in the world market is estimated at only a few thousand pieces.
The color of the emerald can hardly be treated. Internal defects in these minerals are visually removed by filling cracks with cedar oil. Also a special mixture consisting of resins and polymers may be used. The latter improves the appearance of the stone much better than the former. Unlike oil, the polymer penetrates into smaller cavities and gives the stone a better tint. It is therefore not surprising that the cost of such emeralds will be at least 2-3 times cheaper.
The chamber for “oiling” is a sealed vacuum steel vessel. First, all the air is sucked out of the emerald. Then it is immersed in oil and begins to gradually heat to a temperature of about 500 degrees Celsius. It leads to a smooth increase in pressure on the stone. The “warming up” of the emerald occurs within 10-15 minutes, after which it is left off-camera for several hours. Then treated minerals are cleaned from oil residues with spirit, sorted and evaluated. The whole refining process takes about ten hours.
In contrast to corundum, whereby the heat treatment gives a permanent effect, the oiling procedure is reversible. In due course cedar oil (but not a mixture of polymers and resins) in the stone can evaporate or flow out, exposing all its internal imperfections.
Let’s compare three visually identical stones. The first is pure by nature, the second is oiled with cedar oil, and the third has undergone the procedure of improvement with the help of polymers and resins. The difference in price between the first and second stones will be approximately twofold – while between the first and third ones, up to 4-5 fold.
Because of the high cost of emerald raw materials, when cutting a stone, first of all they are guided by its natural size. A cutter tries to keep the maximum possible weight without caring about the recommended parameters of length, width and height. As a result, most stones look ugly, and they can only be rescued by re-cutting.
Since natural emeralds are most often found in the form of hexagonal prisms, as a rule, they are given an «emerald» cut or a derivative of it. Unfortunately, this form reveals all the cracks and inclusions more clearly than any other.
If the crystal is irregular in shape or was split, it can be cut in the form of an “oval”, “cushion” or less often, a ”pear”. There are more facets on the pavilions of such stones, which adds brilliance to the emerald and hides inclusions. It’s for this reason that they cost 20-30-40% less than an emerald cut precious beryl.
These stones are dichroic. This means the bluish-green and yellowish-green colors are viewed from different sides by the crystal growth. Thus the cutter must also make the most accurate calculations and choose the right side that will be showed to the viewer.
Another difficulty of emerald cutting is their possible oiling before giving the stone a shape. As a rule, raw materials are sold in lots. Some unscrupulous sellers mix them with oiled stones in order to get more profit. Checking each emerald is a long and rather complicated process. It’s for this reason that all defects hidden by impregnations are simply not taken into account by the gemologist when choosing the optimal shape for a particular crystal. When cutting, the material heats up to 600 degrees and, in most cases, oil flows out. Thus defects that were not visible earlier are manifested, and beryl can simply crack. However, setting these stones is no less “whimsical”. One awkward movement or wrong pressing often leads to the loss of the mineral.
If you put a ruby and an emerald of the same carat weight next to each other, the former will be noticeably smaller in size, due to a higher density. Therefore, for example, if you are looking for sapphire as a pairing to a four carat emerald, the mass of it should not exceed three carats.
The most authoritative laboratories for an emerald report are the Swiss SSEF and Gübelin. On frequent occasions other certification centers do not see traces of oiling in the minerals, or identify the composition with which the cracks of the stone are filled by mistake. Sometimes they may also overestimate the real characteristics of the mineral.
And the final consumer pays for such mistakes. The amount of oil greatly affects the cost of the stone. For example, an insignificant decrease in beryl cuts around 20% from the price; while the minor ones, around 45% off, and the moderate ones, by 55-60%. All the while a mineral with significant improvements can cost three times cheaper than its untreated “brother”. Therefore, the name of the laboratory that issued the certificate is of importance. And do not forget that emeralds, whether they are bought from a dealer or a well-known brand, must be checked every three to four years by a gemologist and, if necessary, re-oiled.
The topmost stones from the Muzo field, weighing more than 20 carats, cost no more than $200 thousand per carat. They may be more expensive only if set in the jewelry of a famous House, but never in a stone market. For example, on the 27th of May in 2014 at the Christie’s auction in Hong Kong, a ring with a reference Colombian emerald weighing 28.88 carats went under the hammer for $4.1 million, or $142 thousand per carat. Returning to the cost difference between Colombian and Zambian stones, on the 16th of May in 2012, Christie’s sold the ring with an African emerald of 16.59 carats for $105 thousand — if beryl were from a competitive source, its final cost could exceed half a million dollars.