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Russian Gemstones Encyclopedia

Vladimir Bukanov. Russian Gemstones Encyclopedia

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

CHRYSOBERYL (ALEXANDRITE)


CHRYSOBERYL (Chrysoberyll—Chrysobéryl— ’ризоберилл). (Werner, A.G. 1790), from Gk., “chrysos”, gold, plus “beryllos” – beryl, by color and chemical composition. Name used from antiquity for gold-colored beryl.

Composition & Properties. Oxide – BeAl2O4, orthorhombic system. Admixtures: iron (Fe3+), cymophane – chromium (Cr3+). Hardness 8.5. Density 3.7- 3.9. Luster vitreous. Cleavage good, one direction. Fragile. Insoluble in acids. Chrysoberyl occurs as thick tabular, less frequently short columnar crystals with feathery streaks along the crystal faces. Twins and sprocket-like trilling are common. Following diamond and corundum, chrysoberyl is the third mineral by its hardness. Transparent to translucent. Color: yellow, green to bright green, gray, brown, red, violet, bluish-green, less frequently colorless. Color is stable, controlled by chromium and iron admixtures chrysoberyl cat’s-eye and alexandrite, the chrysoberyl varieties, are well-known valuable gems.

Chrysoberyl has gold yellow color and strong luster. After facet cymophane, a yellow to pale green variety of chrysoberyl, exhibits chatoyancy due to presence of hollow channels and acicular actinolite or sillimanite inclusions oriented parallel to long axes of crystals. Cabochon’s cut parallel to such inclusions exhibit silky luster as moved relatively to the light source (due to moving light band). The effect is controlled by reflection of light from channels or inclusions. This variety is called a noble cat’s-eye. Besides, cymophane may exhibit opalescence play of light and asterism. Pale green chrysoberyl cat’s-eye, treated with gamma rays, gains dark brown color.

Alexandrite was named after Alexander II (1818-1881), heir to Russian throne, later Emperor Alexander II on the occasion of his coming of age in 1834. Occurs as short columnar or tabular crystals frequently forming V-shaped intergrowings or pseudo-hexagonal trilling. Color: grass green, bluish-green, greenish-yellow, or brown. Admixture of chromium gives green color; at electric light it has a dense red color due to selective transparency to blue-green and red-violet rays. This feature is called the alexandrite effect, although it is observable in other minerals as well. Strong pleochroism is inherent in alexandrite, i.e., alteration of color along three directions from green via yellow to red at daylight and from green via orange-red to carmine red at electric light. Intensity of the alexandrite color is its characteristic feature. Sometimes it called reverse, from Lat. “versium” – turn. This feature categorizes gems of 100, 50, 25, and, sometimes, 10% grade. Some crystals exhibit zonal color. Chatoyancy occurs at presence of regularly oriented inclusions.

Deposits. Chrysoberyl is typical mineral of pegmatite, skarn, greisen, and essentially micaceous rocks formed after mafites. Fields are major sources of gem-quality chrysoberyl. Alexandrite was first described in Russia (1831) in the Sretenskiy fields, the Urals. However, long before that it was known as vaydhuriam mined from fields in India. In Russia chrysoberyl and alexandrite (so-called Siberian alexandrite) occur in the Izumrudnye kopi, Middle Urals. Findings are most frequent in the south part of the emerald-bearing field. The largest joints of crystals were found at the Krasnobolotnyi mine in 1839 in size up to 10x6 cm. Flattened twins and trilling intergrowings (hexagonal stars) got a local Russ. name peshki. Alexandrite has dense dark green or bluish-green colors (homogeneous, zoned or spotted) and displays well-expressed pleochroism. Cymophane has characteristic greenish-blue tone, occasionally with opalescence and chatoyancy. In the middle of the 19th cent. findings of chrysoberyl were known in the Southern Urals at Chebarkul’ Lake and Pavlovsk mine at the Sanarka River. Recently, chrysoberyl was found to occur in pegmatite veins of the Murzinka-Adui group deposits. Yellowish-green crystals, found in the Lipovka pegmatite field, were as large as 30x7x4 mm., and twins 17x15x7 mm. In the same field a tourmaline-anthophyllite vein contained chrysoberyl in association with phenakite. The same mineral assemblage was found near Neyvo-Shaytanskiy. In the Southern Urals chrysoberyl as an accessory mineral was observed late in 1980’s – 90’s in the Ilmeny Mts. pegmatite, as well as in marble-hosted carbonate veinlets on the Kamenka River. In Southern Karelia chrysoberyl (max. size 8 mm.) is known to occur in Pitkaranta, northern part of Ladoga Lake coast. Besides, findings Helsinki twp, Finland were reported.

Significant chrysoberyl deposits occur in Zambia, Zimbabwe, and Tanzania on Manyara Lake. Olive-green chrysoberyl crystals from Zimbabwe and Tanzania frequently exhibit chatoyancy. In Zimbabwe such chrysoberyl is extracted at St Anne deposit near Miamee, not far from Sandawana emerald deposit. On Madagascar chrysoberyl crystals up to 20 cm. are extracted in Ambatondrazaka area; excellent gem-quality twins up to 10 cm. on Miakanjovato Mt.; also from near Alaotra Lake, all in central part of the island, north-east of Antananarivo. In the south-west of Madagascar alexandrite and cymophane in Sakaraha occur in association with sapphire; and at the Ilakaka deposit, near Ihosy. Chrysoberyl findings were reported from Northern Territory, Australia in the Harts Range region. Alluvial fields on the Tasmania Is. contain alexandrite and sapphire.

Historically, fields serve as a source of chrysoberyl, mainly cymophane, in Sri Lanka (Ceylon) in Ratnapura area and Myanmar (Burma). Cymophane, extracted there, is mainly honey-brown to dark yellow-brown. These fields have been worked since 500 B.C., and in 1292 Marco Polo visited one of them. Along with olive-green and pale violet alexandrite, other gems are extracted there. The alexandrite effect is less obvious in alexandrite from Sri Lanka and Africa due to brownish tone from iron admixture. Highly valuable colorless varieties of chrysoberyl, especially rare large twins were found there. In Thailand the chrysoberyl cat’s-eye is extracted from the Bo Phloi deposit to the north from Kanchanaburi. In India chrysoberyl and alexandrite are known in deposits near Manikkal, south Kerala, and in Orissa. Brazil is another major chrysoberyl-producing country. Cymophane – Brazilian cat’s-eye is of slightly lower grade comparative to Ceylon cat’s-eye. Due to inclusions it is less transparent; its color is darker from grayish-brown to yellow. The first findings of chrysoberyl in Brazil date back to 1880-s, but commercial mining started there in 1975. The first mining objects were deposits Malacacheta and Salinas in Minas Gerais. Later, alexandrite deposits Hematita and Era Nuova were discovered near Belo Horizonte. Alexandrite crystals from the latter deposit are smaller than 1.5 ct. Later Jaqueto and Caranaíba chrysoberyl and chrysoberyl cat’s-eye deposits were discovered in Bahia. The largest found chrysoberyl crystal from Jaqueto weighed 24 kg. Chrysoberyl cat’s-eye and violet alexandrite were extracted at the Pankas deposits, Collatina, Espirito Santo State. Maximum cross-section size of crystals found in Pankas was 22 cm. Brazilian alexandrites vary in color from bluish green to lavender and green. Comparative to the best species from the Urals these ones are more dull and dark; hence the price is about 30% lower. About 20% crystals from Malakacheta deposit display chatoyancy when cut. In the U.S.A. chrysoberyl frequently found in pegmatites of the eastern country. In Maine chrysoberyl twins up to 17x9 cm. from the Hoopers Ledge pegmatite, and sharp gem-quality twins up to 5 cm. are known from Hartford, both Oxford Co.; also in Connecticut – at the Haddam Neck, in New York – at Greenfield Park. In minor amounts of chrysoberyl were found of the western country – in Colorado rough twins up to 14x12x2.5 cm. at Drew Hill, Jeffrson Co.; and light green flattened chrysoberyl crystals up to 3 cm. at the Crystal Mountain pegmatite were found.

Unique findings. Large rounded chrysoberyl crystals from placers weighed several kg. The largest ones were found in Brazil: a 25.2-kg. cymophane and a 6.25-kg. chrysoberyl was found in Gaketo, Bahia; and a 785 gm. gem-quality crystal in Malakacheta, Minas Gerais. A perfect 73 ct. cymophane crystal was extracted in Brazil in 1985. In the faceted kind it weighted 18.5 ct. is well expressed chatoyancy and was purchased by AMNH, N. Y. The largest alexandrite crystal found in Brazil (1828) weighed 8 kg. A 5,000-ct. chrysoberyl crystal sized of a human fist was extracted in Sri Lanka. In India a cabochon-cut cat’s-eye, named “Maharanee” had 58.2 ct. Tabular twin crystals from Colorado were as large as 16 cm. in cross-section. In Russia among the unique findings of alexandrite the famous “Kochubey’s druse” exhibited in the Fersman’s Museum Moscow, is known. It is composed of 22 trilling, total dimensions 20x14x11 cm., total weight 5.38 kg.; dimensions of the largest crystal 9 cm. The largest of the gem-quality alexandrite crystals found in the Urals weighed 106.3 g (531.5 ct.). Due to commercial purposes it was facet into several parts. Gem quality alexandrite, 1925 ct. was found in the Urals in 1999.

Synonyms. Chrysoberyl – Blue alexandrite | Alumoberyl | Chryselectrum | ~ chrysoberyl: asteriated ~, Brazilian ~, Ceylon ~, chrysolite ~, Minas Novas ~ (from Minas Gerais, Brazil); Ural ~ | ~ chrysolite: Brazilian ~, chrysoberyl ~, commercial ~, oriental ~.| Chrysopal | Prismatic corundum | Alexandrite cat’s-eye | Gold color stone obs., Russ. | Zaberzat, obs., Russ.

Cymophane (Gk. “cyma”, wave; and “fainestai”, vary, due to chatoyancy) ~ cat’s-eye: Brazilian ~ (after locality), Ceylon ~ (after locality), Indian ~ (after locality), noble ~, opalescent ~, oriental ~, chrysoberyl oriental ~, precious ~, Singhalese ~ (after nationality living in Sri Lanka). | Chatoyant chrysolite | Opalescent chrysolite | Cyglophane | Kymophane.

Cut gems. Chrysoberyl is a valuable gem. Presumably, “Hope’s Chrysoberyl”, found in Brazil and stored in the collection British Museum, London, has the most striking appearance of all known chrysoberyl. This gem is a 45 ct. peridot color chatoyant cymophane into a rounded shape cut. The same collection comprises a 29.4 ct. yellowish-green chrysoberyl from Sri Lanka. AMNH, N.Y., owns a beautiful yellow-green 74.4 ct. gem of emerald-cut. Two unique chrysoberyls from Sri Lanka are stored in the Smiths. Inst. Wash.: a yellow-green one cut into a shape of a “cushion” 114.3 ct. and a green gem cut into an oval shape 120.5 ct., as well as cabochon-cut cymophane cat’s-eye 171, 58.2, and 48.7 ct. Faceted gems from Brazil, a greenish-yellow 46.3 ct. chrysoberyl and star chrysoberyl 6.7 ct. are the items of the same collection. The largest chatoyant cymophane from Sri Lanka 475 and 312.2 ct. are stored in the British Treasury, London. The State Treasury of Iran owns a 147.7 ct. chrysoberyl cat’s-eye. A description of an unusual dark greenish-brown chrysoberyl 20.12 ct., that simultaneously exhibits chatoyancy and asterism, is available. Faceted alexandrite exceeding by weight 3 to 5 ct. are rare; chrysoberyl cat’s-eye usually have weight less than 10 ct., rarely to 50 ct. The largest alexandrite found and cut in Russia had weight 30 ct. The Smiths. Inst. Wash., owns the largest cut alexandrite 65.7 ct. from Sri Lanka, and two smaller gems 16.7 and 11 ct. of the same origin. Two faceted Sri Lanka alexandrite crystals 43 and 27.5 ct. are stored in the collection of the British Museum, London.

Legends. Chrysoberyl is a birthstone of those born under Capricorn and Libra. It is believed to be unfavorable for Aquarius and Aries. It is related to Saturn, Neptune, and Venus. As a remedy, it stimulates blood circulation and hampers neuroses. Chrysoberyl is a national stone of Portugal. In Russia, alexandrite is a symbol of sorrow and solitude; hence it is called the widow’s stone. In some European countries it was a symbol of love and jealousy. In India it symbolized prosperity, long life, and a protection from diseases. Gamblers praise it, for they believe it helps them to win. Some astrologers suppose this gem should belong to spiritually strong people of Fire (Scorpio, Taurus, and Sagittarius); on the contrary, those born under Pisces, Cancer, and Virgo should not own it. Alexandrite is a traditional present to married couples celebrating their 45th aniversary of wedding. In Sri Lanka chrysoberyl (cymophane) cat’s-eye is regard as a national symbol of the country.

Synthesis. Synthetic alexandrite is produced using the flux technique (melting in lithium molybdate at 1200ºC at slow cooling). This process was introduced in 1964 in the U.S.A.; it still remains as a major one. Commercial production was launched in 1973 in San Ramon, California; in Russia it was started in 1980 at Novosibirsk. Natural or synthetic alexandrite is used as a plate for increase of substance; the process lasts for 7 to 9 weeks. This method gives the best gems. The characteristic feature of the latter is a sheaf-like pattern of the solvent bubbles, flux inclusions, and triangle metal bits. Russian synthetic alexandrite produced in is of high quality; it displays strong pleochroism from a bright bluish-green at natural light to reddish-purple at electric light. American synthetic alexandrite is bluish-green to greenish-blue at natural light and reddish-purple to violet at electric light; UV-rays turn it into scarlet. The flux method is used to grow alexandrite crust on the polycrystalline corundum plates. The largest crystals of synthetic alexandrite are produced using the flux pulled (Czochralski) method. It takes less than a week to grow boules (monocrystal “icicles”) up to 12 cm. long and 3 cm. thick. Kyoto Ceramics Co. has been producing synthetic alexandrite with this method since 1970. Trademarks of their products are Inamori synthetic alexandrite and Crescent Vert synthetic alexandrite. The former exhibits chatoyancy; it is pleochroic from bluish-green at day light to reddish-violet at electric light. Maximum dimensions of crystals grown in Russia (1980) with this method were 100x20x10 mm. In Japan Seiko Co. has been producing alexandrite with the flame fusion process since 1980. Russian specialists from Novosibirsk introduced hydrothermal synthesis of alexandrite in 1980.

Synonyms. Alexandria, firma Creative Crystals, Danville, California, the U.S.A., syn. created alexandrite | Alexandria synthetic alexandrite (red color changes for green at day light) | Inamori padparadschah synthetic alexandrite.

Similar Gemstones & Imitations. Chrysoberyl is simulated with such materials: yellowish-green andalusite, apatite, beryl, diopside, kornerupine, sapphire, sinhalite, tourmaline, chrysolite, zircon, enstatite. Chrysoberyl differs from most of these stones by its greater hardness, density, and insolubility in acids. Alexandrite practically none due to a special alexandrite effect, except for andalusite, which exhibits reddish reflections against the green background. Synthetic alexandrite is the best imitation of chrysoberyl and alexandrite. However, synthetic corundum and spinel with alexandrite effect proved to be more economic here. Natural alexandrite differs from its synthetic analogs in the nature of inclusions. Most common imitations are doublets with upper parts made of red garnet and bottoms of green glass. Synthetic alexandrite resembles synthetic corundum with alexandrite effect. It differs from the natural gem in the nature of inclusions. Thus, American synthetic alexandrite contains acicular and lamelliform crystals and metallic platinum. After the X-rays treatment it becomes black, but in several days its initial color recovers. In gem-quality synthetic alexandrite is widely used to imitate its rare and costly natural analog.

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