Emerald is the most valuable representative of the beryl family. 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. Such a balance is possible with the predominance of chromium and vanadium in the beryl structure. But if this group of elements is adjacent to the iron, the mineral begins to acquire a yellowish tinge, which adversely affects its value. Of the total amount of raw materials found, no more than only 15% of the crystals have a jeweler 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 to be 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 emerald 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. 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 light and are almost never of 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.
Colombian stones from the Muzo deposit, which were imported to Europe from the 16th to 18th century by the Spanish conquistadors, are called old-mine emeralds in the trade. It is commonly supposed that, these minerals come with a pedigree and have better quality than crystals found in the modern day. Therefore, most sellers expect an additional premium for the uniqueness of the offer. However, the age of a stone holds no value, and historical provenance in most cases is unprovable. First, there is no testing system in the world that determines at least the approximate date of extraction of a particular mineral. Secondly, the old emerald often has superficial scratches; therefore it is sold at a substantial discount in order to cover the costs for re-cutting. And, finally, any experienced dealer or collector relies on facts and evaluates the material itself: if the stone is really good, it will be expensive, and if there are multiple cracks and inclusions, no provenance will help the situation.
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 or awkward action by the jeweler can easily destroy the mineral, despite the fact that on the Mohs scale, the emerald gains an impressive 7.5 – 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 struck dealers with 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’s market is estimated at only a few thousand pieces.
Internal defects in emeralds 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 of 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.
If we 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.
Precious beryls 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. Most crystals are given an “emerald” shape, which minimizes the loss of raw materials during cutting, but at the same time reveals all the cracks and inclusions more clearly than any other. If the crystal is not high in quality 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.
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 have been known to overlook 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 less 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. A 18.04 cts Colombian stone, became the most expensive emerald in the world in June 2017 when it was sold at a Christie’s auction for $5.5 million or $305 thousand per carat. Such a high cost is due to the combination of unique characteristics of the mineral and its provenance —it spent more than thirty years in the Rockefeller collection. The previous record was broken six years earlier by the Colombian emerald in a Bvlgari brooch from the Elizabeth Taylor collection. With a weight of 23.46 cts it was sold for slightly more than $6.5 million, or $280 thousand per carat.