Where to find emeralds in the Urals. Natural Green Emeralds: Facts about the Stones
Many mineral lovers wonder where emeralds are mined. Emerald mining was carried out in the Arabian desert back in the times of Ancient Egypt, Greece and Rome. Indians and Persians especially revered this stone. In the 16th century AD. Spanish conquerors brought to Europe magnificent emeralds mined by the Incas in the Eastern Cordillera. The Spaniards also found emerald mines in Colombia, now known as the Chivor mine. The unique Colombian emerald deposits have not lost their great industrial importance to this day.
In 1831, emerald deposits were discovered in Russia, and a little later - in the USA and Australia. Before these discoveries, emerald was an extremely rare stone.
Emeralds are mined on an industrial scale at large deposits in South Africa in the Transvaal, in India in Rajasthan and Zimbabwe, as well as at the Carnaiba mine in Brazil. Currently, the production of artificial emeralds is also popular.
The emerald mined in the Urals is distinguished by its very large size: it is a unique dense green transparent crystal measuring 6.5 × 8 × 12 cm. An even larger crystal (14 × 35 cm) of good quality was discovered in 1956 at the Somerset deposit.
Characteristics and chemical composition of emeralds
The noble emerald, which is a colored variety of beryl, is classified as a first-class gemstone. The ancient Greeks poetically called this mineral “stone of radiance.” Typically, when cutting stones, they are given stepped or multifaceted shapes. If there are defects, cabochons are formed.
The chemical formula of emerald is similar to the composition of beryl Be 3 Al 2 × (Si 8 O 18), however, part of the aluminum is replaced by magnesium and chromium, iron, alkalis and even water are found in small quantities. This crystal often contains many impurities: phlogopite, talc, tourmaline, rutile and others. The mineral owes its characteristic color to chromium; in dark stones its content reaches 0.6%. The yellow tint of this gemstone is due to an admixture of iron. Often this variety of beryl is unevenly colored. The shape of the crystals is usually columnar or prismatic, up to 5 cm in length and 1.5 cm in width.
Main suppliers of emeralds
For the formation of this beautiful mineral, it is necessary that beryl-forming solutions absorb chromium oxides from neighboring rocks: black shales, dunites, etc. Emerald can be found in granitic pegmatites (acidic igneous rocks frozen deep in the earth’s crust), which are located in chromium-containing rocks. The main type of industrial-scale emerald deposits is associated with the interaction of fluorine-rich hydrothermal fluids with hypermafic rocks (ultramafic rocks high in silicon, aluminum, magnesium and iron). As a result of this interaction, emerald-bearing mica phlogopite and biotite-phlogopite bodies are formed. Phlogopite is a mineral of the mica group, a layered silicate with the chemical formula K(Mg) 3 (AlSi 3 O 10 (OH, F) 2. Stones are mined on an industrial scale in the following deposits:
- Jebel Zebrah in Egypt;
- Habachtal in Austria;
- Emerald mines of the Urals in Russia;
- Somerset, Cobra and Gravelotte in South Africa;
- Sandawana, Novello Climes, Chikwanda, Mustard Pepper, Mayfield Farm in Zimbabwe;
- Lake Manyara in Tanzania;
- Rajgarh, Kaliguman, Bubani Muhami in India;
- Minagaora in Pakistan;
- Pune in Australia;
- Carnaiba, Fazenda do Pombo in Brazil.
Emeralds extracted from hydrothermal deposits of carbonaceous carbonates and shales in Colombia are distinguished by first-class quality: Muzo, Chivor, Cosques, Peña Blancas.
Pegmatite emerald deposit
Crystals of this mineral are occasionally found in felsic pegmatites occurring among ultrabasic or other chromium-rich rocks. The pegmatite veins contain small amounts of miarolitic voids containing spectacular druses of microcline (a feldspar mineral), smoky quartz, tourmaline, light green beryl and emerald.
Basically, low-quality crystals with weak color and impurities are mined here. They are used to make cabochons and extract druses for collections. Typical representatives of such deposits are located in North America and Norway. In the USA, there are such deposits in the state of North Carolina. They are not of particular importance, since there are no large deposits here, and the stones are pale in color.
In Norway, 45 km north of Oslo, in Eidsvoll, among the biotite schists, there are pegmatite veins with miarolitic cavities filled with cassiterite - tin oxide; The local crystals are translucent due to small gas-liquid inclusions.
Pneumatolitho-hydrothermal and hydrothermal deposits
Pneumatolithic-hydrothermal deposits are composed of mica rocks, in which green crystals are found located inside hyperbasic rocks. These mines are known in many countries of the world (Zimbabwe, Russia, India, Australia, Brazil, etc.). They are the main reserve of ornamental stones and are confined to altered (metamorphosed) ultrabasic rocks penetrated by pegmatite granites. An interaction of this kind shows the best conditions for the formation of emeralds: as a result of the penetration of gaseous components of liquid granite rocks, which contain beryllium, into chromium-rich hyperbasites.
Emerald-bearing mica is accompanied by pegmatites, plagioclasites, quartz-feldspathic and quartz veins.
These pegmatites, in contrast to the actual pegmatite emerald deposits, are devoid of miaroles and contain only pale-colored beryls.
The class of emerald hydrothermal formations includes the famous and richest deposits in Colombia, and some small formations in Afghanistan and Brazil. Both of them are located at the outcrops of carbonates impregnated with C or Mg, and shale rocks, which contain C and Cr. The source of chromium may be underlying rocks. The origin of emerald veins is granitoid magmatism.
Colombia. The famous emerald deposits of the Eastern Cordillera in Colombia are located in the departments of Boyaca and Cundinamarca, 50-150 km from Bogota. They were developed by the Incas long before the Spanish invasion, and they definitely have the highest percentage of high-grade gemstone jewelry. In total, about 180 emerald mines are known in the area.
Placer deposits of emeralds
This type of deposit, unlike pneumatolytic-hydrothermal deposits, does not make a significant contribution to the jewelry industry, and therefore there is not much information about it.
The low prevalence and poverty of emerald placers can be explained by the small number of primary deposits and the structural and morphological type of primary emerald-bearing bodies unfavorable for the formation of placers, represented, as a rule, by thin mica veins with steep dip angles.
Some role is played by eluvial and eluvial-deluvial placers and debris, mined during the initial period of exploitation of the deposits. There is evidence of the presence of alluvial placers in Zimbabwe in the area of the Sandavana and Samambula Forest deposits, in the area of Faciendo Seo Tiano (Bahia State, Brazil) and near Melville (New South Wales, Australia). Of great interest are the recently discovered alluvial placers of emerald in the Jacopi region (Colombia) with small crystals, sometimes of the highest quality.
In ultraviolet light, emeralds have a red glow - this is a way to distinguish them from other similar stones. The high value and rarity of the emerald stimulated the production of all kinds of imitations, of which the most common were doublets made of green beryl or garnet with quartz or glass, glued together with green gelatin. Often other, less valuable minerals, such as green sapphire (“oriental emerald”), are passed off as emerald.
Emerald is the last mineral among the highest class of gemstones (if you take into account the Mohs scale). In Sanskrit and Persian, the name of this stone sounded like “zammorod” and “zumundi”, which meant “green”, and in Old Slavonic emeralds were called “smaragd”.
But the English word emerald appeared only in the 16th century. There is a version that this is the name given to all minerals that are green in color.
Emphasizing the aristocratic nature of the stone, its “inaccessibility” and transparency, people nicknamed the gem green ice.
What did emerald do to deserve such a reputation?
Mysteries of history
Like many other gems, green minerals sometimes became the makers of history.
So, at the beginning of the 16th century, conquistador Fernando Cortes wanted to give his bride five rare emeralds. The minerals were distinguished not only by their unsurpassed quality, but also by their special shape in the form of a rose, bell, goblet, horn and fish. In order to get the stones, a desperate Mexican stole them from the Incas.
Cortes did not know that Queen Isabella of Castile, who became his mortal enemy, was hunting the stones with him. The story of the emeralds only added fuel to the fire of the then raging struggle between two clans for the Spanish throne. However, none of the jewel hunters were victorious.
In 1541, the unique stones mysteriously disappeared.
Igneous mineral
Emerald is of igneous origin and is a type of beryl. However, it is easy to distinguish from other stones of similar color due to its high degree of purity and transparency, as well as its cool shade of green.
Along with diamond and ruby, it is considered one of the most expensive minerals. According to the law “On Currency Regulation” in Russia, this stone is equated to freely convertible currency, that is, it can be exchanged for any foreign currencies, act as payments in international transactions, and also participate in trading on the main foreign exchange markets. Unlike many other beryls, emerald is quite soft. Therefore, if products with green minerals are stored incorrectly, the stones lose their original shine and become dull.
Colorless oil or oil tinted with green pigment will help to enhance natural emeralds and give them a special shine. This method is often used by jewelers from different countries.
Many years ago, the German physicist Goldschmidt, while studying the mineral, discovered that the color of an emerald depends on the amount of chromium or vanadium impurities.
Natural stones, as a rule, have many defects, so it is quite difficult to find gems in nature that are ideal in purity and shade. Thus, during mining, minerals weighing hundreds of carats are found, but have no jewelry value. At the same time, rare pure bluish-green emeralds can cost more than diamonds.
The most valuable emeralds are called “antique”. These stones have a rich dark green color, which samples mined from new deposits do not have.
In nature, there are many minerals similar to emeralds: green garnet, jade, tourmaline, tsavorite, fluorite and other stones of a similar shade. How not to confuse them?
You can distinguish emerald from other green gems using a refractometer. This special device measures the refraction of light that occurs in a particular stone. The emerald indicator is approximately 1.58 units.
Modern technologies
Most often, gem-quality emeralds are relatively small in size, but modern production often uses artificially grown or synthetic minerals. The main growing methods are flux and hydrothermal. To do this, the crystals are placed in an environment whose temperature is about 600 degrees Celsius, and the atmospheric pressure can reach up to 1400 atm.
Jewelers also use the ancient technology of making doublet stones, connecting two small emeralds or an emerald and some other mineral.
Emerald is one of the few stones after which a certain method of cutting minerals, widely used in jewelry production, was named.
This is a type of step cut, in which the stone is given a rectangular shape with beveled corners. The emerald cut protects even the most fragile minerals from damage and chips, and also advantageously represents the color of the stone and its purity.
Southern Stone
When valuing expensive stones, their location often plays an important role. So, for example, Kashmiri ones are considered the best, Burmese ones are considered the highest quality rubies, but Colombian ones are recognized as the standard emeralds. It is in Colombia that the famous Muso mines are located, where amazing bright green minerals are mined.
The famous Etbay deposits of Jebel Zubara and Jebel Sikait are located in a mountain range on the Red Sea coast at an altitude of 550 m.
In addition, precious minerals are mined in Eastern and Southern Africa, Egypt, India and Pakistan. In Russia, the Urals are famous for their emerald deposits.
Experts can recognize the “nationality” of each stone by special inclusions characteristic of minerals of a certain country.
In addition to Colombian ones, gems from Zimbabwe are also especially valued, which are still cheaper than standard stones.
Star image
Having never lost its value, this precious mineral is still very relevant today. In the right frame, even classic ones sound new and modern.
Most often the stone has a gold frame. Supplemented with diamonds, jewelry with emeralds looks sophisticated and elegant. Such products will be a wonderful accent to your evening look.
Emerald jewelry may well become a family heirloom. Luxurious gems are preferred by style icons such as Sherlize Theron. Sharon Stone, Beyonce, Cameron Diaz, Dita Von Teese and others.
Svetlana
Despite its impeccable beauty, emerald is a very fragile stone, capable of breaking even from a slight blow. In order to prevent damage to the stone, jewelers have come up with a special cutting method in which the stone is given a rectangular shape with beveled corners. Emeralds can easily be scratched by their stronger counterparts: topazes, diamonds, alexandrites, sapphires and rubies. Therefore, it is better to store jewelry with emeralds separately from other jewelry. The emerald cut, care when wearing and storing, have made this stone a favorite among many women.
Svetlana
Emeralds are gemstones, a type of the rare mineral beryl. In terms of their beauty and cost, they can easily compete with diamonds. They can also surprise you with facts about themselves. The Roman Emperor Nero used large emeralds instead of lenses to watch gladiator fights. Queen Cleopatra was very fond of emeralds. Receiving this stone, decorated with the queen’s profile, from her hands was considered a manifestation of the highest favor of the ruler of Egypt.
Alexander Sergeevich Pushkin had a talisman - a ring with a large square emerald, to which the great poet dedicated the poem “Keep Me, My Talisman.”
Svetlana
Bright green foliage and freshly fallen snow - these colors belong to different seasons, but look surprisingly harmonious together. This is the first association that comes to mind when you see such a set of gold with emeralds and diamonds or cubic zirconia. Complement a green blouse and white trousers with a set of gold jewelry with emeralds and your look will only be enviable.
Svetlana
Emeralds have been known since ancient times - the first mention of their mining dates back to the 37th century BC in Ancient Egypt. Nowadays, most emeralds are mined in Colombia. There is also a deposit in Russia - these are the Ural emerald mines. Not only emeralds are found here, but also apatites, alexandrites and other precious stones.
Emerald mining was carried out in the deserts of Arabia during the times of the ancient Egyptians, Greeks and Romans. These stones were mainly revered by Indians and Persians. In the 16th century, Spanish conquistadors brought beautiful green stones to Europe. The Spaniards also found Colombian emerald mines, which to this day have not lost their important industrial and jewelry value. In 1831, deposits were opened in Russia, where Ural emeralds were mined, and later in America and Australia. Before all these discoveries, emeralds were considered extremely rare stones found in nature. Let's find out in more detail how and where exactly beautiful emerald stones are mined.
As already mentioned, mining of the mineral has been carried out since ancient times. In some sources, the place where the first deposit was found is called the Arabian Desert, in others - the Namibian Desert. It was there that the “Cleopatra mines” were found, which for unknown reasons were closed for a long time and reopened only towards the beginning of the 19th century.
Another famous ancient deposit was the mines near Aswan, which is not far from the Red Sea. The mention of him takes us back to the reign of Sesostris III, that is, more than three thousand years ago! The Egyptians made mines two hundred meters deep; four hundred miners could hardly fit there at the same time. In those distant times, it was believed that the mineral was afraid of any light, so its extraction was carried out in its complete absence. After being extracted, the emerald in the rock was broken into pieces and then smeared with olive oil. Then, in this way, they made it easier for themselves to select “stones of green radiance.”
In Colombia they are grouped in a wide band crossing the ridges of the Eastern Cordillera in a northwesterly direction, but the total area of this band is unclear. The richest sites are those of Muzo in the center of the strip and Chivor in its extreme south. Small quantities of emeralds were mined at various points in the emerald-bearing region. The larger of these points are the Cosquez and Peña Blanca fields north of Muzo.
Geological structure of Colombian emerald deposits, despite their intensive development, very little is covered in the literature. And although their sharp difference from the deposits of the Urals was noted long ago, the details of the geological structure of the deposits were not very clear. In this sense, the research of A. Beus turned out to be extremely useful. They clearly showed that the main emerald deposit - the Muzo region - is very specific. The basis of the area is composed of Lower Cretaceous carbonaceous shales (Villeto Formation), weakly metamorphosed and therefore highly soiled. Productive layers, capas bueno (good layers), are practically indistinguishable from unproductive ones (cambiado - others). Only the presence in productive shales is indicated albita. According to A. Beus, productive layers are confined to fault zones through which solutions that caused mineralization could flow.
The richest in the Muzo region at the time A. Beus visited it was the Tekuendama quarry, which is a steep, almost hundred-meter cliff, composed of soot-black schistose rock, intersected by a network of thin veins and streaks of calcite. Miners work in the quarry without technical guidance, without worrying at all about the mining system. In many areas of the quarry, collapses are possible, threatening the lives of miners.
Among the mined stones, a distinction is made between esmeralda - a high-class jewelry stone and moraya - emerald green - a low-quality material. Local experts believe that to extract 1 carat of Moraya it is necessary to process about 1 m 3 of slate, but to obtain 1 carat of Esmeralda it is necessary to process about 12 m 3 of slate.
The Chivor mine, well described in recent years by the American Johnson, is composed of the same Lower Cretaceous shales (Cokueso Formation) as Muzo, but more variegated in composition. Clayey black and yellow shales are interbedded with black limestones and white and pink mudstones. Among the shales, three horizontal layers (?) stand out - “iron belts” containing pyrite or goethite(brown ironstone) pseudomorphs on pyrite. Productive layers lie between the “iron belts” or near them, moving no more than 50 m away. In productive shales, as in the “iron belts,” the presence of albite is noted. Emerald-bearing veins cut schists in all directions, but unlike Muzo, calcite veins do not contain emerald. Emerald contains pyrite and albite veins or veins in which these minerals are present. The best stones in the deposit are found in pockets, sometimes associated with veins located in shales. The pockets may be hollow or filled with albite, pyrite or goethite. The best stones were found loose, in a void. Calcite, although common in Chivor, forms very beautiful specimens in places with pyrite, but emerald is never found with calcite. Johnson notes , that there are no igneous rocks or pegmatite veins in the area of the Chivor deposit.
One can only regret that there is no scientific research into the emerald deposits of Colombia. Everything is important here - studying the nature of the host rocks, finding out the reasons for the difference between Chivor and Muzo, and, of course, searching for sources of beryllium and chromium. I can't believe that Colombia is the only area where such low-temperature emeralds are found. It would be nice to look for them in other places, but where is not yet clear.
Emerald deposits in Russia
The emerald mines of the Urals are located somewhat north of the city of Asbest, along the same strip of ultra-mafic rocks with which the Bazhenov asbestos deposits are associated. The most detailed study of these deposits was undertaken in the 20s of this century by Academician A.E. Fersman, who gave a very informative description of these mines, subsequently clarified and supplemented by K.A. Vlasov. By the time A.E. Fersman began his work, the mineralogical nature of emerald had already been fully studied and it was confidently proven that the green color of emerald is associated with the dissolution of chromium in mineral beryl. True, there is not much chromium here, but it is still there. It was this combination of beryllium and chromium in one mineral that then presented the main difficulty in understanding the origin of this mineral.
Just at the beginning of the 20s in our country, Academician V.I. Vernadsky and A.E. Fersman, who was a friend and student of V.I. Vernadsky, laid the foundations of a new discipline - geochemistry, which examines the prevalence of various elements in different geological conditions. One of the first firmly established geochemical laws was that in nature some elements are distributed in a strictly regular manner. Thus, elements such as fluorine, tungsten, tin, rare alkalis and especially beryllium. Actually, there are very few of these elements in the granite rocks themselves, but when the granite magma cools and crystallizes, these elements accumulate in the last portions of the melt and are released either in pegmatite veins, if these volatile substances cannot escape from the crystallization area, or in altered rocks - apogranites or greisens, replacing pre-existing minerals along the path of their movement.
The second group of strictly specialized elements are elements such as nickel, cobalt, platinum, palladium and chromium, which are closely associated with silicic acid-poor ultramafic rocks.
Research by A.E. Fersman in the Emerald Mines of the Urals made it possible to show the reason for this combination. He established that the mineralization of these mines was formed as a result of the intrusion of relatively younger granitic magma into pre-existing ultramafic massifs. Granite, which penetrated here, is apparently a branch from the massif developed to the north, with which numerous pegmatite veins of the Murzin-Adui strip are associated. This may indicate that the granitic magma that intruded in the Emerald Mines area was quite rich in volatile substances in general and beryllium in particular.
Having assumed the intrusion of granitic magma into ultramafic rocks, A.E. Fersman was here for the first time to clarify the contact zoning that arose at such contacts. A thorough study of a number of sections allowed him to determine that as a result of the intrusion of granite around it in the ultrabasite, the following reaction series arises:
- pegmatite or granite;
- biotite mica (thickness up to 1.5 m);
- chlorite-actnolite zone (up to 1.0 m);
- talc slate (up to 3 m);
- unaltered ultramafic.
Three intermediate zones (2, 3, 4) arise as a result of the interaction of granite and ultrabasic rock. Of course, this is a very rough diagram; in nature everything is much more complicated. Individual zones become thinner, and sometimes they simply fall out. Sometimes the vein itself disappears; only volatile substances remain from it, creating contact zones, etc.
If this section, however, is compared with other cases of contact between granitoids and ultramafic rocks, then the complete identity of all contact zones can be seen quite clearly.
This issue is considered to one degree or another when describing deposits jade And jadeite.
The interaction of granite melt and ultrabasic rock also explains the unusual geochemical association of beryllium with chromium - beryllium was brought from granite, and chromium was borrowed from ultrabasic rock. Also extremely interesting are the observations of A.E. Fersman on the distribution of minerals in the contact field. Pegmatite minerals, such as beryl, apatite , fluorite, occur either in the igneous rock zone or in mica. However, when beryl forms crystals among the minerals of a pegmatite vein, they are colorless or have an aquamarine character; beryl acquires an emerald green color only when it crystallizes among mica. It is interesting to note that at the deposit many factors indicate a low temperature of beryl formation. To a certain extent, this brings together the Ural and Colombian types of emerald deposits.
The presence of chromium only in beryl in micastones clearly shows that both granite and ultramafic material participated in the formation of the mica zone. The mechanism of this formation is less clear. According to A.E. Fersman, the granite melt, enriched in volatile substances, which penetrated into the ultrabasite (Fersman calls it pegmatite), intensively dissolved the ultrabasite substance and actively heated the nearest contacts. Due to the melt enriched in the ultrabasic substance, mica crystallized, a mica zone appeared, inside which a section of almost unchanged melt may remain, crystallized in the form of granite or a melt depleted in silicic acid in the form of quartz-free rock - plagioclasite. Due to the heated rocks, into which the solutions still introduced silicic acid, zones of amphibole and talc.
Later, it was suggested that the contact zones formed after the solidification of the pegmatite vein; the vein and the ultramafic rock that host it were exposed to solutions that caused their recrystallization and transferred the substance of the vein to the ultramafic rock and back. Very unclear ideas were also expressed. Thus, one young researcher recently wrote that emerald-bearing mica “are mica of the greisen facies.” Frankly, it is difficult to understand the difference between this “new” view and the “old”. Greisenization, especially greisen containing fluorite and beryl, is caused by the action of residual solutions rich in volatiles on one or another pre-existing rock. Here, in the Emerald Mines, and according to A.E. Fersman, there are no real pegmatites, there are only some relics of granite, enriched in volatiles, and their effect on ultrabasite. So what's the difference? Dont clear. But every dispute in the spider reveals new facts and usually benefits the truth; it is likely that this dispute will ultimately be beneficial.
The description of the Emerald Mines of the Urals, made by A.E. Fersman, was very interesting, clear, surprisingly simple and well explaining all aspects of the formation of emerald. This description attracted the attention of researchers studying the gemstone abroad. They began to purposefully look for emerald in contacts between granite pegmatite veins and ultrabasites. After the publication of the works of A.E. Fersman, emerald deposits were discovered in South Africa (South Africa), Zimbabwe and India. All these deposits are very close in genesis to the deposits of the Urals.
African deposits
In South Africa, emeralds were found in 1927. The area where they were discovered emerald deposits, is located on the southern slope of the Murchison Range, on a slightly hilly plain, the geological basis of which is the ancient Archean system of Swaziland, which includes a sequence of granites, gneisses, amphibolites and ferruginous quartzites. Numerous pegmatites are confined to this sequence. Emeralds are confined to mica surrounding pegmatites. The first to be opened was the Somerset mine, located 12 miles east-northeast of Gravelot station. Later, the Cobra mine and a mine near the station were opened in the same area. However, Somerset appears to still be the largest. The amount of emerald mined in Africa is not clear; it is only indicated that in 1936 14,081 carats of emerald were mined here.
Emerald in India was identified in 1944 by Dr. H. Cruikshank, based on samples obtained by geological surveyor Bagchand Soni during the expansion of mica and beryl mining during the war years. Later, primary deposits were also discovered, forming a large strip in southwestern Rajasthan, stretching from the city of Ajmir to the south-southwest. The largest deposit in Kuban is located somewhat northeast of this city. A little southwest of the city is the Rajar deposit, and even further southwest, already in the area of Mewar, there are several smaller deposits: Kaniguman, Teki and Gum-Gura.
All these deposits are confined to a highly dislocated zone in local Precambrian deposits, along the boundary between the rocks of the “Delhi system” and the more ancient rocks of the Aravali. In the fault zone, isolated sections of ultramafic rock outcrop and numerous pegmatite veins and veins occur tourmaline granites It is assumed that these are younger “post-Delhi” formations associated with the Erinpur granite located in the same area. It is extremely interesting that many pegmatite veins containing beryl are associated with the Erinpur granite.
In the area of the deposits, biotite and muscovite shales, actinolite and tremolite rocks, as well as talc shales are associated with pegmatites. Unfortunately, the available sketches are very unclear, and it is not possible to establish the sequence of reaction zones. It is noted that emerald is found only in mica schists. Only uncolored beryl is found in pegmatites. The great similarity of all deposits in the region is specially noted.
The weathering imposed on all deposits greatly complicates the study and understanding of emerald formation processes in India. There is strong kaolinization of feldspars and vermiculitization of biotite. The first work in the area was carried out specifically to study resources vermiculite. The number of emeralds mined is not very clear; it is indicated that in 1945-1947. More than 900 pounds of emeralds were mined in India per year. It is unknown how much emerald jewelry there was. The emeralds at the mine are roughly sorted, purified in acids and alkalis, coated with a layer of fat and then auctioned in Jaipur.
The last most interesting find, although of only mineralogical significance, was the discovery of an emerald in Ukraine in 1971. Here, among tremolite and tremolite-actinolite schists - products of ultramafic metamorphism - a vein of well-differentiated albite pegmatites was encountered. Develops around pegmatite biotite -phlogopite rim 15-20 cm thick with swellings up to 30-50 cm. Bright green emerald crystals up to 1.5-2.0 cm in size are found in the mica rim. The color is caused by the presence of some chemically determined chromium in the emerald. The pegmatites themselves contain weakly colored beryls, which, like the local emerald, contain quite a lot of alkalis.
Emerald is an interesting gemstone. Of particular interest is that this mineral is associated with geochemically very different elements: chromium, a typical element of ultramafic rocks, and beryl, an equally typical element of acidic rocks. The conditions under which the combination of these geochemically incompatible elements is possible were brilliantly deciphered by A. E. Fersman, and now one can see that many emerald deposits of the world - India, South Africa, Egypt and Ukraine, as well as the very small Habachtal deposit in the Alps, o which was not mentioned - they have exactly the same character as the Ural Emerald mines, and were formed by the contact action of granite on ultrabasite.
In light of these results, the nature of the Colombian deposits is particularly interesting. It is not yet clear where beryllium and chromium came from in these deposits and how crystals of beryl containing chromium could have arisen in calcite veins among the shales. Until now, the synthesis of emerald is carried out under conditions of high temperatures and pressures. For Colombian deposits, however, it can be assumed that beryl crystals grow at significantly lower parameters. Obviously, further intensive research work on the synthesis of emerald should be carried out in this direction.
