How much does 1 carat of alexandrite weigh?

Let us turn again to the book by M.I. Pylyaev, where the author writes: “Immaculately good crystals are extremely rare, and if they are found, the completely transparent part of the stone usually does not exceed one carat in weight.” And this is 1877! The book by F.F. Zolotukhin, V.I. Zhernakov, M.P. Popov “Geology and patterns of distribution of precious stones of the Malyshevsky deposit (Ural Emerald Mines)” provides the following data. Of the 855 cut stones, only 18 pieces (2.1%) were classified in the weight category from 0.5 to 0.99 carats. The total weight of the stones of this group was only 16.9 carats, or 0.09% of the mass of alexandrite raw materials mined during the year. It becomes clear why the famous US National Mineral Collection contains a faceted Ceylon alexandrite weighing 65.08 carats, while the largest Ural stone in the collection is less than 5 carats, and contains cracks visible to the naked eye. Robert Genis notes that any alexandrite exceeding 10 carats is exceptionally rare (Gemstones Forecaster Vol.22, No.1, 2004). In July 2009, James L. Sweaney published a photo (see below) sent to him by a dealer friend from a mineralogy show in Tucson. The photo, taken with a cell phone camera on the sidelines of the show, shows the “Alexandrite Godzilla,” a stone weighing 27.71 carats. The owner of the stone, who impressed those around him as a secretive person, claimed that alexandrite was of “Russian” origin. The cost of the stone and the terms of the sale were not publicly announced, which prompted those present to assume that the deal, if it took place, would be kept secret. At the deposits of the Ural Emerald Belt, alexandrite in ore bodies is most often found in the form of crystals, which are the accretion of three individuals. They are tabular in shape with the faces of two truncated hexagonal pyramids. The Ural miners called them “pawns.” In addition to pawn-triples, alexandrite forms twin accretions and separate individuals. But they are much less common.
In the photo: on the left are untreated alexandrite crystals (“pawns”), on the right is an intergrowth of crystals on mica. Malyshevskoye field, Ural. Lighting with incandescent lamp. Alexandrite “pawns” have a rather complex internal structure. This is due to manifestations of the twinning process. Twin sutures divide alexandrite crystals into 6 sectors, which usually have a common central area of ​​turbidity with numerous mineral and gas-liquid inclusions. The sectors have synchronous zoning, fracturing and internal stresses. The sizes of alexandrite crystals vary widely: from millimeters to 5–6 cm in diameter. Many alexandrite crystals contain mica-phlogopite inclusions, and sometimes they are simply overflowing with them. Unlike emerald, alexandrite is more fragile and has the property of splitting in a certain direction, so most of its crystals are heavily fractured. The color of alexandrites and chrysoberyls is often zonal and spotty; it happens that alexandrite forms a thin surface crust on the crystal and goes deeper into ordinary chrysoberyl. As it becomes clear from the above, the master cutter faces a responsible and very difficult task, since clean, uncracked areas in alexandrite crystals are found extremely rarely. As a rule, the “cutting” zone is located on the periphery of the crystal, since its central part is opaque – “clogged” with flakes of mica and other minerals, as well as gas-liquid inclusions. “Knocking out” a clean piece of 1 carat from a pawn is a great success! If we take into account that during subsequent cutting and polishing, from 40 to 70 percent of the initial mass of the workpiece is wasted, it becomes clear why the vast majority of faceted alexandrites weigh less than half a carat. In a batch of 855 stones cut in 1899 by “The New Emeralds Company” (data from F.F. Zolotukhin, V.I. Zhernakov, M.P. Popov “Geology and patterns of distribution of precious stones of the Malyshevsky deposit”), the proportion of stones with weighing more than 0.5 carats was only 2%, and the average weight of one stone from the batch after cutting was 0,23 carats. Look, here is that prophetic Russian stone that I told you about! Tricky Siberian! he was still green, like hope, and by evening he was covered in blood. From the beginning he was like this, but he kept hiding, lay in the ground and allowed himself to be found only on the day of Tsar Alexander’s coming of age, when a great sorcerer, wizard, vadelota went to Siberia to look for him. Leskov N. S. Alexandrite. The beauty of gems has always been one of the greatest mysteries. But precisely because there is so much mystery in them, they are cited as epithets in world literature and even in the Holy Scriptures. RubeusMilano brand necklace with Ural alexandrite (a stone from Lazurit-D) of more than 10 carats, tanzanians, an overcoat and diamonds at the presentation at the Museum of Decorative and Applied Arts in Paris. Alexandrite is a type of chrysoberyl – beryllium-containing mineral from the subclass of complex oxides of the BeAl composition₂O₄. It has unusually strong pleochroism. The peculiarity of alexandrite is its ability to change color under different lighting from bluish-, yellowish-, brownish-, grayish-green – in daylight and violet-, orangeish-, brownish-, crimson-, -red in artificial (incandescent) light. This ability is called the “Alexandrite effect”. The color of alexandrite and the features of the reverse manifestation (the alexandrite effect itself) are mainly due to variations in the content of both the main coloring impurity elements – chromium and iron, and minor impurity elements, which primarily include copper, manganese, titanium, nickel, vanadium and cobalt (Bukanov, 2012). The morphological type of alexandrite is dominated by rhombic-bipyramidal and short-prismatic crystals; thin- or thick-laminated individuals are also found. There are both single crystals, V-shaped or X-shaped intergrowth twins and pseudohexagonal (hexagonal) intergrowth tees. Most often they form germination tees and single crystals (Gromalova 2010). The most famous alexandrite druse, found in the Emerald mines of the Middle Urals, consisting of twenty-two well-formed tees, is stored in the Mineralogical Museum. A.E. Fersman RAS in Moscow (Fig. 1). Transparent crystals of alexandrite without inclusions and cracks are rare. The main physical and optical properties of alexandrite are presented in Table No. 1. Rice. 1 Intergrowth of alexandrite crystals “Druze of Count Kochubey” from the collection of the Mineralogical Museum named after. A.E. Fersman RAS. 8.5 (Mohs scale) glassy, ​​at the break – greasy conchoidal or uneven – clear in prism, – pinacoid imperfect, – weak in pinacoid np = 1.732 – 1.747, nm = 1.734 – 1.749, ng = 1,741 – 1,758 Behavior under ultraviolet radiation inert, moderately red in short and long wavelengths Chrysoberyl as a new mineral was identified by A.G. Werner in 1790. Before this, it was considered chrysolite (a jewelry variety of olivine). Chrysoberyl from the Urals was first reported by Professor D.I. Sokolov in the “Guide to Mineralogy”: “During his visit to the Ural emerald mines, chrysoberyls, crystals of extraordinary size, were discovered in this very mountain.” A series of studies followed, since Ural chrysoberyl was a very rare mineral and had exceptional dichroism, but the term “Alexandrite effect” had not yet been applied. Later, in 1862 N.I. Koksharov restored the historical moments of that time: “. those days (1834, April 17), when all of Russia celebrated the coming of age of the heir to the throne, the now safely reigning Emperor Alexander II, chrysoberyl was found in the Urals, completely different from all other colored varieties of chrysoberyl. Due to its excellent qualities, the new mineral soon took one of the first places among the most expensive minerals. This precious stone, on the occasion of a memorable day, is named in honor of His Imperial Majesty, our greatest monarch, alexandrite, at the suggestion of the famous mineralogist E. Nordenskiöld” (Leikum et al. 2010). Until the eighties of the 1880th century, the Ural Emerald Mines were considered the only deposit of alexandrite. Shortly after the discovery of the Ural alexandrites in the 80s, the Morawaka deposit in Sri Lanka became the second classic source of large, cutable, color-changing alexandrites. Today it is mined in the rivers and alluvium of the Ratnapura province and in some other areas of the interior of the island. In Brazil, information about alexandrite finds appeared back in the 1975s of the XNUMXth century, but its industrial mining began only in XNUMX. In the state of Minas Gerais, placers with chrysoberyl were first mined deposits of Malacacheta and Salinas, and then alexandrites were discovered in the deposits of Hematita (Hematita – it was developed quite quickly), Nova Era, near Belo Horizonte, Carnaiba, Minaku region (Goy state), Esmeraldas de Ferros. In India, chrysoberyl and alexandrite are found in deposits in the states of Orissa, Andhra Pradesh, in the south of Kerala, near Manikkal. In Western Australia, alexandrite is mined in river placers of the Puna deposit and on the island. Tasmania, and also near the city of Daurin. In Africa, these are, first of all, the famous Somabula and Masvingo deposits (formerly Fort Victoria) in Zimbabwe. In Tanzania – the Lake Manyara and Tunduru deposits, and is also found in all beryl deposits, mainly of the placer type. On the island of Madagascar there are placer deposits near the settlements of Ankatsobe, Antananarivo, Ambositra, Alaotra, Sakahara. Deposits are also known in Zambia and Zaire. Alexandrite is found in pegmatite areas in the west of the Mogok valley in Sakangi or Barnarmo, as well as in placers in the vicinity of Mogok, the towns of Kyatpyin and the village of Barnarmo (Gerasimova et al., 2019) Large crystals (over 2 carats) of good quality are quite rare. The key, price-determining, so to speak, characteristics for faceted alexandrites are: origin, color and degree of alexandrite effect, weight, purity and cut quality. The most valuable are Ural stones that change their color from bright bluish-green to crimson or violet-red with a minimum number of inclusions, preferably with their absence and with good reverse. Brazilian alexandrites can compete, since they have the desired color and generally good quality, but the right of primacy can still be assigned to Russian alexandrites, since this mineral was discovered in Russia. Particularly valuable are alexandrites that have a “cat’s eye” effect, which is caused by the presence of needle-shaped inclusions oriented parallel to each other. Rice. 2 Ural alexandrite in daytime and “evening” lighting (stones from the Lazurit-D collection). Natural alexandrite is characterized by inhomogeneities, cracks, gas-liquid inclusions of irregular acute-angled shape, as well as mica flakes (Fig. 3). Rice. 3 Network of cracks and inclusions of different origins (a), mica flakes (b) in natural alexandrite from the Malyshevskoe deposit. Since the extraction of alexandrites at different times was small, synthetic stones (artificial alexandrites and imitations) appeared on sale. The most common imitations of alexandrite are synthetic corundum with vanadium additives, which is characterized by a color change from purple-blue to pink, and synthetic spinel, which has a characteristic color change from green to gray. At the beginning of the 20th century industrial synthesis of imitations of alexandrite and more was successfully carried out by the Dzheva factory in Switzerland. There are various methods for synthesizing alexandrite, the most common commercially used being the Czochralski method, zone melting and flux method. The color of such alexandrites is caused by an admixture of chromium and is close to the color of natural alexandrites. Characteristic features for synthetic alexandrites are needle-shaped inclusions (Czochralski method), flux inclusions, triangular, hexagonal metal particles, straight growth lines (flux method Fig. 4), gas bubbles or twisted, funnel-shaped elongated inclusions (so-called strands) are characteristic for the zone melting method. Rice. 4 Flux inclusions (a) and linear zoning (b) in synthetic alexandrites grown by the flux method. The synthesis of alexandrites was actively used in the second half of the 300th century, they were grown by Creative Crystals in California and were sold at a fairly high price of 500-6000 dollars per carat; in comparison, prices for natural alexandrites in the USSR could be sold at prices from 20 to 000 dollars per carat (adapted from Elwell, 1981). The cost of natural alexandrites today is very high. According to the GemeWizard database, the cost of good quality alexandrite can reach 46 thousand US dollars per 1 carat. In 2018, an alexandrite from Sri Lanka weighing 29.41 carats with an average color change intensity was sold at Christie’s auction for $256 (Fig. 568a). In 4 In 6.1, a cabochon-shaped alexandrite ring with a distinct color change, weighing approximately 140 carats, sold for $901. A 6.35-carat heart-shaped alexandrite ring with a distinct alexandrite effect (changing color from neon greenish blue to purple) sold for $111.5 thousand (approximately $18 thousand per carat = RUB 1) (Fig. 200b). Rice. 4. a. Alexandrite weighing 29.4 carats (photo from www.christies.com); b. Ring with 6.35 carat heart-cut alexandrite and diamonds (photo from www.sothebys.com). The precious stone alexandrite can rightfully be considered one of the most valuable stones in the world, and for Russia a real mineralogical symbol (Fig. 5). Rice. 5 A unique transforming necklace of the RubeusMilano brand with the largest faceted Ural alexandrite (stone from Lazurit-D) weighing 69.37 carats was first shown at a presentation at the Museum of Decorative and Applied Arts in Paris on July 1-2, 2019. On the left is a photo under artificial lighting, on the right in UV rays. Bukanov V.V. Colored and collectible stones. Encyclopedia. S-P.: Granit, 2008. 472 p. Gerasimova E.I., Kupriyanova O.I., Lastochkina A.A. Collection of the State Geological Museum of the Russian Academy of Sciences for the 260th anniversary of the museum. 2019 Gromalova N.A. Solution – melt crystallization and a comprehensive study of the composition, crystal morphology and properties of chrysoberyl and alexandrite, Dissertation for the scientific degree of candidate of geological and mineralogical sciences. M.: Moscow State University named after. M.V. Lomonosova, 2010. 255 p. Leikum M.S., Albrekh V.G., Popov M.P., et al. The mysterious stone of Tsar Alexander (about alexandrite, Alexander II and not only about them). Internet publication, 2010. 376 p. Elwell D., Artificial gemstones. Moscow: “Mir”. 1981,