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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

ZIRCON


ZIRCON (Zirkon—Zircon—÷иркон) (Werner, A.G. 1783), from Arabic (in turn from Pers. “azargun”) “zar” – gold and “gun” – colored, referring to one of the many colors that the mineral may display. Known from antiquity.

Composition & Properties. Silicate – Zr[SiO4], subclass orthosilicates, tetragonal system. Hardness 7.5; for amorphous ones – 6. Density 4.7; for amorphous ones – 3.6-4.2. Diamond luster, for amorphous ones – glass luster. Cleavage in one direction. Fragile. Often radioactive. Zircon is found as well formed crystals, which shape depends on the conditions of its forming. In granite pegmatites they are long columnar, and in alkali pegmatites – short columnar bipyramidal. Transparent to nontransparent. Transparent crystals are not more than 1 cm. long; bigger ones – up to 10 cm., they are usually non-transparent. Color: red, orange-red, orange, reddish-brown, yellow, gray, green, more rarely – blue, and the most rarely they are colorless. Colored crystals display pleochroism – from bright to pale tones. distribution of color is often zonal-sector one. The nature of their color is connected with electron-hole centers and ionic admixture: yellow – iron (Fe3+), red and light blue – uranium (U4+), green – zirconium (Zr4+) and also cadmium (Gd3+), thorium, hafnium. According the composition of admixtures they classify such varieties of zircon as – oyamalite with Y2O3 up to 17.7%, naëgite with Nb2O3 up to 7.5% and others. According its color transparent zircon has special names: reddish-brown one to yellow-orange – hyacinth (hyacinte), brown one – zirconite, orange-red one – topaz hyacinth, honey-yellow one – melichrysos, straw-yellow one – jargon, light blue one – starlite or stremlite, colorless one – acroite. Color of starlite is not stable, because it is usually received with annealing. With regularly oriented micro-needled inclusions there is the effect of cat’s-eyes in faceting zircon – zircon cat’s-eye and burnt zircon cat’s-eye. Sometimes it displays brownish opalescence, reminding asterism, or aventurescence. The effect of cat’s-eye in zircon can also depends on parallel-oriented tube inclusions, and in annealed zircon – on disc-shaped cracks, which are oriented in parallel to the long axis of a crystal. Non-transparent amorphous varieties have grass green to dark green or brown-green color. Such amorphous zircon with radioactive admixtures and H2O has the name arshinovite, auerbachit or pseudo-zircon. Radioactive gamma zircon is amorphous because of high content of admixtures of uranium, thorium, rareearth, and H2O. According the shapes of crystals, gamma zircon can be columnar – cyrtolite or double pyramidal – malacon.

Deposits. Zircon is found in the composition of magmatic and metamorphic rocks. Its gem-quality crystals are found mainly in pegmatites, but they are extracted usually at placers. In in 1880-s in Russia gem-quality zircon was extracted in the Middle Urals, from placers in the regions of Koltashy and Kornilov log. In the Urals it was known in syenite pegmatites of the Ilmeny Mts. and Vishnevye Mts. and at placers. In 1837, in the Ilmeny Mts., South Urals, they found a crystal of zircon, 20 cm, long, 2,739 gm. Recently, at a placer on the Cheremshanka River they found a unique crystal, 22 cm. long, 3,558 gm. Average length of zircon crystals is 2-3 cm., but completely transparent crystals are usually shorter. At the Vishnegorskoye placer the content of zircon available for faceting was not more than 10%, the size of them reached 10x7x7 cm. On the Kola Penin., near Lovozero Lake, collection rough material exists at the Vavnbed deposit near the Vavnbed Mt. There, in the zone of albitization of nepheline syenites, from 10 to 60 m. thick in layers, the content of zircon crystals in the extracted rock sometimes reached 10%. Its non-transparent, short-columnar crystals were from 0.2 to 9 cm. in cross-section. Their distribution in albitites was irregular: from separate crystals to nest accumulations. In the nests zircon reached the maximum size; sometimes there were half-transparent crystals. Other findings of zircon crystals on the Kola Penin. are known at the El’ozero locality on Keivy Range, Enskoye and Kovdor deposits. In carbonate veins of the southern part of the Enskoye iron-ore deposit honey-yellow crystals of zircon reached 2 cm. in cross-section. In Transbaikalia, in Slyudyanka area, in pegmatites of the Kop’ Pilipenko crystals of zircon up to 8 cm. was found. In Primorskiy Region, in the Bol’shaya Ussurka River zircon is extracted together with sapphire from goldfields, which were formed in the process of washing away of the weathering crust of alkali basalts. There, between the basins of the rivers Bol’shaya Ussurka and Bikin, along the Kedrovka River, at the Nezametnoye they found at placers gem-quality sapphire and hyacinth. Orange-red and red-brown crystals of hyacinth reached 5 cm. in length there. In Yakutia, brown and rose-yellow hyacinth, not more than 1 cm. in size was extracted as additional material at the diamond pipes Zarnitsa, Mir and Udachnaya. The biggest faceted stones from the material of the Mir diamond pipe reached 9 ct. In Kyrgyzstan placers with hyacinth were discovered at the Dolon deposit, in the upper reaches of the Karaunkur River, on the south slope of the Baidula Ridge. There a valued resource of zircon is supposed to be 28 thousand ct. of gem-quality material. In Uzbekistan, zircon at placers on the Kafirnigun River was discovered.

In the North Norway, near Alta, Finnmark, found crystals of zircon up to 5 cm in length. In South Norway, there is the Seiland zircon deposit, and in alkali pegmatites near Larvik, Vestfold, and Arendal, Aust-Adger, were found columnar crystals of zircon up to 100 gm. In France, near Espaly, Haute-Liore Dept., Auvergne, they discovered placers with red zircon. Such findings are known at deposits of Great Britain and Italy. In Tanzania, at the Emaly deposit zircon as white pebbles is extracted at placers. After faceting they received colorless stones. There is information about zircon deposits in Zimbabwe. In Lesotho, at the diamond pipe Sekameng columnar crystals of violet-red zircon up to 1 cm. were found. In Mosambique, brown crystals zircon up to 10 cm. in Alto Ligonha region are mined. On Madagascar, zircon is found mainly at sapphire deposits in the southern part of the island. There, in the Betroka region crystals of red and green zircon, up to 14x8x8 cm. they extracted. In the southeastern part of the island, also at the Itrongay deposit, Fianarantsoa Prov., zircon in orthoclase-microcline pegmatites is found. In Saudi Arabia there is the deposit of zircon Jebel Tuwalah. In Australia, in the Northern Territory, at placers they find gem-quality red-brown hyacinth in crystals up to 2 cm., and at the Alice Springs deposit the size of its crystals reached 10x8x6 cm. In Eastern Australia, at the Ballenmerry deposit zircon at placers is pale colored, yellow-brown and green. At the Anakie deposit, Queensland, at placers with sapphire crystals of Australian zircon are small, rarely up to 1 cm. long. Their color is from pink, light violet to brown-red and thick violet-red. There is information about the extraction of orange zircon at placers of New South Wales, near Maji, as well as on Tasmania – Tasmanian zircon and on the Campbell Is., to the south from New Zealand. In South-Eastern Asia, the main deposits of zircon are placers of Indochina Penin. On Sri Lanka, at placers near Ratnapura and Matara they found zircon crystals of different color, up to 9 cm.: colorless – Matara diamond, or Ceyloni diamond, green – amorphous zircon, or Ceylonian zircon, zircon cat’s-eye. Faceted stones with aventurescence, which depends on small disc-shaped cracks, were made from them, as well as star zircon up to 24.92 ct., green zircon with the effect of cat’s-eye up to 5 ct., brown-gray and yellow zircon. In Thailand, significant quantities of golden-yellow zircon were extracted at the Chantabury deposit. In Southern Vietnam, in the region of Kha, they found natural variety of blue zircon – starlite. In Cambodia, zircon deposits are exploited near Pailin, Battamang Prov.; in the north of the country – in the region of Rowieng, at the Pnomtnuon deposit; in the north-eastern part of the country – in the Styngtraeng Prov., at the Bo Khea deposit, where they receive the best gem-quality zircon. In Myanmar and South Korea, yellow and green zircon is extracted as additional material at placers of other gemstones. In China, on the Hainan Is., red and brown-red hyacinth is extracted. In India, in the Orissa State there is a deposit of pink-violet zircon with needle inclusions of dark brown rutile and flakes of hematite. In the Jammu and Kashmir State (disputed area), in the Shigar River Valley, near Astor, they extracted red zircon. In the U.S.A. gem-quality zircon in several states was discovered, it was mainly orange-brown. In the western part of the country good crystals to 20 cm. occur in Pacoima Canyon, Los Angeles Co. In the east – it is at Mineville, Essex Co., New York. In Pennsylvania very fine crystals up to 4 cm. in serpentinite at the Williams quarry, Northumberland Co., were found. In Canada, at the Lake Clear deposit, near Kuehl Lake, Renfrew Co., and also at the Sebastopol deposit, Ontario, crystals of non-transparent hyacinth up to 40 cm. and 8 kg. were found. In the Québec Prov., zircon at the Matilda Lake was found. In Brazil zircon on Jaguaraçú at placers together with native platinum are extracted.

Synonyms. Azorite, after the discovery location on the Azores Iss., Portugal | Bedjadi, Arabic, also for topaz, obs. | Calyptolite | Cerkonier, obs. | Cyrtolite (cirtolite), from Gk. “cyrtos” – hooked and “litos” – stone, after the shape of amorphous crystal from deposits of Sri Lanka | Diochrom, local name in Italy at the Monte Somma deposit | Engelhardite, after Russ. scientist V. Engelhardt | Gomeda, Hindu. | Heldburgite, after the discovery location near Heldburg, Thüringen, Germany, obs. | Hussakit, after Germ. chemist E. Hussak, obs. | Ceylon jargon | Kaliptolite | Leucochrisos, obs. | Ligure (liguiriy), obs. | Naëgite, after the deposit in the region of Naegi, Gifu Pref., Japan | Octorutile, after the shape of crystals | Orvillite, obs. | Ostranit, from the Brevik deposit, Norway | Oyamalite, after the Oyama deposit, Japan | Polykrasilith, from Gk. “crasis” – mixture, obs. | Râhuratna, Sanskrit, – that is, the jewel dedicated to the mysterious “dragon” | Ribeirite, after Brazilian scientist I.K. Ribeiro.

Colorless – Dutch bort, from South Africa, obs. | Matara diamond (Matura diamond), after the discovery location near Matara, Sri Lanka | Unripe diamond, obs. | Yamaguchilit, after the Yamaguchi deposit, Japan | White zircon, obs. | Yamaguchilit, after the Yamaguchi deposit, Japan | White zircon, obs.

Red-brown – Fatis, Old Russ. | Hyacinth, from Gk. “hyacinthus” – after the name of the flower and the mythological person | Handsome hyacinth, obs. | Jacinth (jacinph) | Jargoon (yargon), obs. | Peradole (peridol) obs. | Unripe ruby, obs. | Vermeil (vermilion) – general obs. name for orange-red gemstones, including almandine, topaz, cinnabar and spinel | Zirconite.

Yellow – Unripe diamond, obs. | Hyacinth topaz (hyazinthtopas, Germ.) | Jargon, from Arabic “jar” – gold and “goon” – color, after its hue | Melichrysos, from Gk. “meli” – honey and “chrysos” – gold, after its hue, obs. | Lyncurion (lyncurite, lyngourion), anc. Gk., from Lat. "lynx urine" | Lynx stone, obs.

Green — Arshinovite, after Russ. mineralogist A.A. Arshinov | Auerbachit, after Russ. mineralogist I.B. Auerbach | Beccarite after O. Beccari, who brought this mineral from Sri Lanka | Malacon, from Gk.  “malacos” – mild, amorphous.

Light blue – Siam aquamarine, mist. | Starlite (star-lyte), annealed, from Chantaoon deposit, Thailand | Siam zircon, from Indochina, faceted in Thailand.

Quality improvement. Natural color of noble zircon is usually thick red-brown or dark green, that’s why they make it lighter in color with the method of annealing under the temperature of 800-1000°C. During this procedure oxidation of iron (Fe2+ to Fe3+), and of niobium (Nb4+ to Nb5+) take place. When they are being cooled slowly, yellow zircons become colorless, honey-brown ones – red-violet; and when they are being cooled fast, green ones become blue. In the restoration environment they receive yellow and colorless zircon. Color, which is received with annealing, is not always stable. Such zircon has its own names – fire zircon or burnt zircon. Completely decolorized zircon is called Matara diamond, or sparklite; blue one – blue zircon, or Siam aquamarine. The method of annealing has been known from the deep antiquity, when they decolorized zircons putting them in pieces of carbon or boiling it in nut oil. This method is used also to make non-transparent amorphous varieties lighter in color. Decolorized zircon has stronger luster, but it receives brownish hue with time.

Cut Gems. Zircon was known in Ancient Rome, it was mentioned by Pliny the Elder. In the collection of gems in the State Hermitage, SPb. there are several cameos on zircon, including an image of Fortune – 2.2x1.2 cm., 3-2 centuries B.C., the East Mediterranean region; a man’s and a woman’s profiles – 1.9x1.4 cm., Italy, 16th cent.. Zircon was especially valued in the 15-16ss cent., when it was brought to Europe at first. Annealed colorless gemstones were used in place of diamonds, which was reflected in their names – Ceylon diamond, or Ceylon brilliant, Matara brilliant. To distinguish them from yellow zircon, the last one was called jargon, or Siam diamond, and brown-red variety – hyacinth. Then, the name hyacinth became common used for other gemstones of the similar color, for instance, vesuvianitebrown hyacinth, or Vesuvian hyacinth; pink corundum – Viennese hyacinth; sapphire – oriental hyacinth; hessonite – Ceylon hyacinth. In 1783 only, the Germ. mineralogist A.G. Werner classified zircon as a separate mineral. A new wave of interest to gem-quality zircon came in 1830-s. However, even nowadays, it is often undervalued as a gemstone.

Faceted zircon displays strong diamond luster, bright play of color and the effect of fire because of its high dispersion. Colorless zircon is faceted in the brilliant pattern; colored one – in the step pattern of faceting or in combined pattern: the upper part – in the brilliant pattern, the bottom part – in the step pattern. The mostly high evaluated is faceted green zircon; it is a rare collection gemstone. As an ornamental variety of zircon-containing rock we should mention basalt with inclusions of radial-rayed clusters of zircon crystals and crystals of xenotimechrysanthemium stone. In Japan, it is used as an ornamental stone – kiku-kwaseki, or kiku-ishy.

Famous Gems. A collection of unique faceted zircons is in the Smiths. Inst., Wash. Among them there are stones from Australia: a brown one – 21.2 ct., a brownish-red one – 31.1 ct.; from Sri Lanka: a green one – 23.5 ct., colorless ones – 23.9 and 48.2 ct., a yellow-brown one – 97.6 ct. and a brown one – 118.1 ct.; from Myanmar: a red-brown one – 75.8 ct.; from Thailand – a blue one – 103.2 ct. and a brown one – 105.9 ct. In the AMNH N.Y., there is a perfect blue-green faceted zircon, 208 ct., and a rare zircon cat’seye, 20.6 ct. In the Royal Ontario Museum there is a brown zircon – 23.8 ct. and light blue ones – 61.63 and 17.8 ct. In the Geol. Museum, London there is a blue zircon – 44.27 ct., a golden one – 22.67 ct., a red one – 14.34 ct. and a colorless one – 21.32 ct. In the Museum Hist. Nat., Paris, there is a green zircon from Sri Lanka – 63 ct.

Legends. According a Gk. legend, a son of a king of Sparta was called Hyacinth. He was a friend and a favorite of the god Apollo. When he taught a young man to throw a disc, the god of wind Zephyrus changed the direction of its flight, and the disc blew Hyacinth’s head. Drops of his blood transformed into thick red stones – hyacinths. In the ancient times hyacinth served as an amulet against poisons and infections. According the Bible, hyacinth is one of the 12 stones, which decorated the breastplate of the high priest of Israel. In the medieval symbolic hyacinth meant wisdom, Catholics treated it as a symbol of humility. The Christianity devoted pink hyacinth to the apostle Simeon. In Russia, it was a stone of merchants, actors and also thieves, because they thought it could make a person invisible. As a talisman, hyacinth gives safe way to a wanderer as well as it provides hospitality in any hotel. Astrologers suppose hyacinth to be a stone of planets Saturn and Neptune, and a lucky stone for those who were born under the sign of Capricorn.

Synthesis. Synthetic zircon is received with the hydrothermal method, as well as from the solution in melted material and with the method of gas-transporting reaction on basic structures. Its color is formed with different admixtures: europium – colorless, iron (Fe3+) – brown, praseodymium – pale yellow, terbium – yellow, manganese (Mn2+) – rose, cobalt – red, neodymium – pale purple, vanadium (V5+) – pale blue, chromium (Cr3+), and copper – green. Colored synthetic zircon for jewelry purposes is produced by the firm Jevahirgjan, Switzerland.

Similar Gemstones & Imitations. Zircon looks like aquamarine, diamond, vesuvianite, hessonite, demantoid, cassiterite, monazite, rutile, sapphire, sinhalite, spessartine, titanite, topaz, tourmaline, and chrysoberyl. As imitations of zircon, they use synthetic spinel, phianite (cubic zirconia) and glass.

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