Emerald deposits were formed as a result of orogenesis (mountain folding), which 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). This 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, when the extracted crystals were transported for further processing to specialized centers, 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, the first place is undoubtedly for 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 the Zambian deposits 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, in the Malyshev mine in the Urals, which recently resumed the 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.
The color of the emerald can hardly be treated. Internal defects in these minerals are visually removed by filling cracks with cedar oil, as well as a special mixture consisting of resins and polymers. The latter improving the appearance of the stone much better than the first (unlike oil, the polymer penetrates into smaller cavities and gives the stone 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, which in turn leads to a smooth increase in pressure on the stone. The «warming up» of the emerald occurs within 10-15 minutes, after which the off camera is left for several hours. Then treated minerals are cleaned from oil residues with spirit, sorted and evaluated, and 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, one of which 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.
An interesting fact: if you put a ruby and an emerald of the same carat weight next to each other, the first 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. This among many other things you will only have heard from an experienced specialist, who helps to avoid mistakes and make a better choice in terms of price and quality. If you want to try your luck and do it on your own, ask for at least a certificate of authoritative laboratories, the best of which in the evaluation of emeralds are the Swiss SSEF and Gübelin.Unlike them, the GRS laboratory does not often see traces of oiling in the minerals or identify the composition with which the cracks of the stone are filled by mistake. GIA, considered the most authoritative estimator of diamonds, is also weak in working with precious beryl — sometimes it may overestimate the real characteristics of the mineral. Certification centers that do not specialize in emeralds physically cannot evaluate them correctly. And the final consumer «pays» for such mistakes, because the amount of oil greatly affects the cost of the stone. For example, insignificant decreases 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.