How to understand synthetic emerald?

The green variety of beryl, known as emerald, is so attractive and so desirable to own that the successful synthesis of this variety was of more than just scientific interest. Even the modest success of experiments on the recrystallization of rubies from fragments of natural stones was quite encouraging for researchers who carried out similar experiments with crushed beryls; the color, which changed when heated in a flame of detonating gas, was restored by the preliminary addition of a small amount of chromium oxide. However, these experiments failed: when melted, glass was formed each time, not a crystal; therefore, it was a sad mistake to call such items scientific emeralds, since they were neither emeralds, much less scientific. They differed from true emeralds, firstly, in color, although green, but the color of the leaves, and not a real emerald, and, secondly, in physical properties – refractive index (1,508-1,527) and specific gravity (2,417-2,489), which were slightly lower than that of emerald crystals. The production of beryl glass by melting beryl fragments in a flame of detonating gas is not an innovation: indeed, it has been known since the beginning of the last century , but did not attract the attention of jewelers until the moment when the possibility of obtaining synthetic stones was established. The first successful experiments in the synthesis of emeralds were apparently carried out by Otfel and Perret . During long and complex experiments on making various beryllium silicates, they managed to obtain tiny emerald crystals. They achieved the best results by placing a mixture of beryllium, silica and alumina (in proportions corresponding to the composition of beryl) under a coating of lithium dimolybdate in a platinum crucible, which was placed in an autoclave. The temperature, after being raised to a gentle heat and maintained at that level for 24 hours, was raised to almost 800° C., and held at this point for 15 days. It turned out that the temperature should not exceed 800°, since otherwise beryllium silicate phenacite Be will be formed instead of beryl Si04. In the first stage, the lithium compound gave crystals in the form of octahedra, then, as the temperature increased, the octahedra were replaced by prismatic beryl crystals, and finally, when all the octahedra disappeared, larger prisms, as a rule, grew at the expense of small ones. At the end of the experiment, after cooling, the mass was crushed and, dissolving it in dilute hydrochloric acid, beryl crystals were released. It was found that the crystals, free of inclusions (as far as possible), have a specific gravity of 2,67 and their composition exactly corresponds to the formula of beryl. At a temperature of 750°C, the crystals were obtained in the form of short tabular hexagonal prisms, and at 800°C they became more elongated, so that their length was either equal to the diameter or exceeded it by 1,5 times. The addition of chromium to the mixture gave the crystals a green tint as bright as that of the best natural emeralds; if the additive amounted to 0,001 of the mixture, the chromium oxide was completely absorbed by the crystals, and if it reached. 0,003, then most of the chromium oxide remained in the containing mass. The shape of the crystals was almost perfect, although too small for jewelry purposes. In 1911, the IG Farbenin Industry company in Bitterfeld began experiments that began with repeating the experiments of Otfel and Perret; the first individual crystals of synthetic emeralds suitable for cutting were obtained almost 20 years later; They were marketed under the brand name “Igmsrald”. No detailed messages at that time. this was not published, but in 1942 the production of stones ceased, and then a description of the process appeared. Crystals were grown from a melt of BeO, Al , adding lithium acid molybdate as a flux, in a platinum crucible that was heated by electricity. It turned out that a necessary condition is the absence of supersaturation of the mixture, which occurred when all three components were distributed evenly, as a result of which only small crystals were formed. Therefore, silica was supplied in the form of crushed quartz, placed on a platinum grid at a short distance from the bottom of the vessel. Reproducing the true emerald color has encountered some difficulties (additive Cr gave a bluish-green tint), but in the end it was possible to obtain a druse of crystals with the same excellent color as the best natural emeralds, and large enough to produce stones weighing at least one carat when cut. Igmerald clearly showed brighter fluorescence under ultraviolet light than natural emeralds. In addition, the refractive index, birefringence and specific gravity of synthetic emeralds have been found to be below the lowest values ​​observed for natural emeralds (see table on page 199). Almost simultaneously with the experiments carried out by Farbenin Industry, Carroll F. Chatham began experiments in a research laboratory near San Francisco. He grew the first artificial emerald weighing one carat in 1935, and from 1940 the production of industrial products was established. A rough crystal weighing 1014 carats was donated to the Smithsonian Institution for its gem collection, and another, weighing 1275 carats, was donated to the Harvard Museum. Details about the process of making such stones were kept strictly secret; it became known only that crystallization occurs slowly. For some time it was thought that this was hydrothermal synthesis, but now it is believed that the crystals are grown from a melt. The appearance of clusters of crystals immovably attached to the crust indicates that seeds are not used. Refractive indices, birefringence and specific gravity, like those of igmerald, are lower than those of natural crystals. Light refraction
ordinary.
extraordinary ray
Synthetic
Lechleitner
Natural.
Transvaal
Aquamarine and Yellow Beryl Morganite Tethyan stones exhibit an intense red color when viewed through a Chelsea filter or crossed filters, and a fiery red color under ultraviolet rays. In 1963, two new artificial emeralds appeared on the European market: one was made by W. Zerfass from the city of Idar-©berstein, Germany, and the other by P. Gilson from the city of Pas-de-Calais in France. As with the Chatham stones, the production process could only be speculated upon, and it was initially assumed that both emeralds were grown hydrothermally (this has certainly appeared in the literature regarding the Gilson emeralds). However, a comparison of the properties of igmerald, Chatham, Zerfass and Gilson emeralds with each other and with the properties of stones recently obtained by the Linde company by crystallization from a melt with the addition of anhydrous lithium molybdate, indisputably indicates that all these stones were made by flux melting. All of them are characterized by generally low constants, which distinguish them from natural emeralds. In addition, under a microscope with low magnification or under a strong magnifying glass, characteristic bual-like formations are observed in them (photo 14), consisting of flux inclusions, often with gas bubbles. The refractive index of the flux (either glassy or crystalline) is higher than the refractive index of the host crystal. Synthetic emerald was also obtained using the hydrothermal method. This process is believed to have been used by E. Nacken in Frankfurt around the century. 1928, although in some characteristics the stones he made are similar to igmerald and other artificial emeralds, believed to be obtained by flux melting. In 1960, J. Lechleitner of Innsbruck, Austria, produced what appears to be the first synthetically coated complex beryl. These stones consisted of faceted pieces of colorless or lightly colored beryl, on which a shell of synthetic emerald was naturally grown by hydrothermal means. The name “emerite” was proposed for them, later replaced by the name “simerald”. Their refractive indices (1,575-1,581), birefringence (0,005-0,006) and specific gravity (2,68-2,71) were higher than those of other artificial emeralds, and were within the same limits as those of natural crystals. Liquid inclusions in hydrothermal crystals such as those described above have a low refractive index, close to the refractive index of water. Among the varieties obtained later were those in which the emerald shell was protected by an additional coating of beryl before polishing. Deeper colored crystals were made as follows: a layer of emerald was sandwiched between layers of beryl, and then the stone was covered with another shell of emerald; synthetic crystals were obtained on a seed from a natural crystal that was then removed as a result of repeated growth of shells of an artificial substance. The complex structure of all these stones can be discovered by carefully studying them under a tenfold magnifying glass or under a microscope, examining mainly the crystal placed on its edge, parallel to the tabular face. Recently, the Linde company produced a high-quality artificial emerald using a hydrothermal method. The cultivation was carried out in several stages, and the seed was ground and removed. To ensure rapid crystal growth, the seed plates are cut at an angle to the optical axis. Optical constants (. 0,006) and specific gravity (2,67-2,69) are within the same limits as the values ​​characteristic of natural emeralds; It was possible to achieve both excellent color and high optical qualities of synthetic emeralds. Their characteristic property is intense red fluorescence. A small quantity of synthetic beryl, colored with vanadium (without chromium) in a bright grass-green color, was obtained by hydrothermal processing by Crystal Resources of Melbourne, Australia. The constants of these beryls almost coincide with the constants of the crystals obtained by the Linde company, but in the absorption spectrum there are characteristic differences from natural emeralds: there are no thin lines of chromium in the red part of the spectrum. Other colored “fake” beryls were made in the USSR and Australia, including light green (Ni), grayish green (Mn), light blue (Cu), dark blue (Fe), pinkish brown (Co) . Claims that the emerald was synthesized by directly heating beryl in a burner flame at atmospheric pressure should be viewed with some suspicion, since beryl is believed to melt incongruently (as has recently been confirmed)*; However, recently, beryl powder has been reported to crystallize to form individual crystals at high temperatures and pressures. To determine what origin – natural or artificial – an emerald has, you first need to carefully examine it under a magnifying glass with tenfold magnification or under a microscope and determine whether it contains inclusions. The three tests described below have been important in the past to verify the origin of emeralds. While the specific gravity and optical constants of natural emeralds vary depending on the nature and amount of impurities, there is a remarkable consistency in the physical properties of synthetic stones due to the fact that they are made from pure substances. In order to check the specific gravity, you need to prepare a heavy liquid, for example by diluting bromoform so that a piece of quartz floats in it. In such a liquid, all natural emeralds will sink, and old artificial stones will float. Another test that is easy to carry out is to immerse stones in an immersion liquid of refractive index n = 1; Benzyl benzoate is usually used for this. Older synthetic stones have a lower refractive index than this value, while natural emeralds have a higher refractive index. Finally, the third test is to test fluorescence using a Chelsea filter, crossed filters or an ultraviolet lamp. Earlier synthetic stones have sharp, and some later ones have extremely sharp, fluorescence compared to natural emeralds (some natural stones have no fluorescence at all). However, recently obtained stones somewhat obscure this picture. The refractive indices, birefringence, and specific gravity of some of the more recently produced artificial emeralds (especially hydrothermally grown varieties) are within the range of values ​​found in natural emeralds. Sharp fluorescence was actually eliminated by adding iron (which can be detected in the spectrum by clear bands at 4270 A The word “emerald” comes from the Greek “smaragd” and means “green stone”. The color green has always been the personification of life and beauty for many peoples. In ancient Rome, this color was the color of the gods. Green is the color of Islam.

History of the origin of emerald

The word “emerald” comes from the Greek “smaragd” and means “green stone”. The color green has always been the personification of life and beauty for many peoples. In ancient Rome, this color was the color of the gods. Green is the color of Islam. Artificial emeralds were first produced in 1928 in Frankfurt by IG-Farbenindustry. Then the production of artificial emeralds was established in France and Russia. Now we can say with confidence about artificial emerald that this crystal is an analogue of natural emerald.

Differences between artificial and natural emerald

They can be distinguished from natural emeralds by certain physical characteristics – density and refraction of light. Synthetic emeralds luminesce differently than natural ones – with a brownish light; natural emeralds do not have this property. The main method for producing high-quality artificial emeralds is the hydrothermal method. It is in this method that all the conditions are created under which emerald is created in nature, that is, at high pressure P = 1,5 kbar and a temperature of at least 600 ° C. Beryl is used as a raw material. Artificial emerald acquires its rich color with the help of impurities – chromium and vanadium. The entire growing process lasts 4 weeks. The price of artificial emerald can be 5 or more times lower than natural emerald. Artificial emeralds can be obtained in different weights and lengths. Today, the equipment used in the cultivation of artificial emeralds has improved significantly, although the entire technological process has remained the same. As you know, natural emeralds have a large number of cracks and inclusions, and are also subject to mechanical stress. Artificial emeralds do not possess these features. Almost always artificial emeralds are saturated dark green or bluish-green, at the same time they are perfectly transparent. The purity and transparency of artificial emeralds create the unique beauty of the stone’s shimmer in sunlight. These qualities of artificial crystals are explained by the fact that they do not contain various kinds of impurities and inclusions. The beauty of artificial crystals is as popular as natural ones, so artificial emeralds are often used in jewelry.

Features of emerald production

To imitate emerald, beryls or high-quality crystal are used. The optical properties of these materials are completely different from natural emeralds. However, it is not too bad to have a fake emerald jewelry if you know that it is an imitation and the price matches it. It is much worse if you buy an “emerald” that is not an emerald. There are many natural green crystals similar to emerald. It is impossible to say that tsavorite, chrome diopside, peridot or green tourmaline are stones that do not deserve admiration. No, not at all, but these are not emeralds, and the price for them is different. Other entries Gold is a precious metal that will never lose its relevance. It is from it that the largest number of jewelry is made, and gold products are the most popular among buyers. However, today you can find a large number of fakes. Amber is the fossilized resin of coniferous trees that has lain in the ground for tens of millions of years. Discussing its meaning for humans. The pectoral cross is one of the most mysterious decorations for those uninitiated in the secrets of religion. The Ardos store has prepared a guide for you that will answer all important questions.

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