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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

SCHEELITE


SCHEELITE (Scheelit—Scheelite—Ўеелит) (von Leonhard, K.C. 1821), after Karl Wilhelm Scheele (1742-1786), a Swedish chemist and apothecary, who proved the existence of tungsten oxide in the mineral in 1781; a discoverer of chlorine, barium, manganese, and, especially, of oxygen.

Composition & Properties.Wolframate – Ca[WO4], tetragonal system. Hardness 4.5-5. Density 5.9-6.1. Greasy luster to diamond one. Perfect cleavage in one direction. Fragile. It forms a row of constant miscibility with powellite – a mineral of the class of molybdates. It is found usually in the form of bipyramidal crystals of pseudo-octahedron shape, as well as in the form of table crystals, grained aggregates and confluent masses. Translucent, rarely transparent. Color: grayish-white, yellow, orange, reddish, brownish, greenish, violet, colorless. With the admixture of MoO3 up to 24% it is golden-yellow molybdoscheelite, or seyrigite; with the admixture of CuO2 up to 7% – green copper scheelite, or cuproscheelite. Inclusions of minerals in scheelite sometimes produce asterism, and admixture of molybdenite leads to black color. A typical feature of scheelite is its bright light bluish-white luminescence in the short-waved ultra-violet rays.

Deposits. Scheelite is formed at contact-metamorphic deposits, in metasomatic rocks, pegmatites, hydrothermal veins, it is accumulated at placers. Among numerous deposits, we mention those with large, well-formed crystals. In Russia, on the western slope of the Subpolar Urals Mts., at the Pelingichey-3 deposit of rock crystal, they discovered translucent yellowish-orange crystals of scheelite up to 4.5 cm. long. In the Middle Urals, near Yekaterinburg, at the Kedrovskoye deposit, they discovered crystals of scheelite up to 8 cm., and at the Berezovskiy deposit – crystals of red scheelite up to 10 cm. in cross-section, up to 600 gm. in weight. On the Chukchi Penin, in the region of the Iul’tin deposit, at the valley of Tenkergyn, they described reddish-orange crystals of scheelite up to 5 cm. in cluster with cassiterite. Findings of large crystals of scheelite were registered at the Tyrnauz mine in Kabardino-Balkaria; at several deposits of Transbaikalia; and in the Primorskiy Region – at the Vostok-2 deposit, near Bikin.

In Kazakhstan, at the Karakamys deposit, Pribalkhashia, they found crystals of scheelite up to 12 cm. long, up to 320 kg. in weight. There, at the Bektau-Ata deposit, they found half-transparent crystals up to 8 cm. In Uzbekistan, well-formed crystals of scheelite were discovered at the Lyangar deposit, Samarqand region. In Tadzhikistan, at the deposits Chorukh-Dayron and Maykhura, near Khûjand, to the north from Dushanbe, the size of scheelite crystals in skarns reached 9 cm. Among other countries, we should mention Czech Rep., where crystals of scheelite were extracted at the deposits Cínovec and Horní Blatná (form. Platten). In Romania, at the deposits Cavnic and Baja Sprija, light bluish and gray crystals of scheelite up to 3.5 cm. were growing on quartz. In Austria, Salzburg, at the deposits Dunkelklamm, Sonnblick, Velibertal and Habachtal, Tyrol, where the size of scheelite crystals reached 10 cm., the weight – 3 kg. In Switzerland, in alpine veins of the Tavetsch deposit, Graubünden canton, they discovered scheelite in the form of transparent colorless crystals up to 5 cm. In Germany, dark yellow crystals of scheelite are known at the Altenberg deposit, Erzgebirge Mts., Saxony. In Spain, crystals scheelite up to 10 cm. in cross-section at the Estepona deposit, Prov. de Málaga, they extracted. Besides, crystals of scheelite were extracted as additional material in Italy, in Piedmont – at the Traversella deposit; in England – on the Cornwall Penin. and in Cumbria; in Sweden – at the Sörhårås deposit, near Ultevis, Norrbotten.

In the western part of Kenya, brown scheelite was extracted at the Kuiva deposit, near Kakamega. In Namibia, in pegmatites near Natas, transparent crystals scheelite up to 50 kg. weight were extracted. In the south of Madagascar, in pegmatites of the Ambondrombe deposit, they discovered large crystals of molybdoscheelite. In Australia, at the Georgiana mine, Queensland, they found crystals of cuproscheelite; and in Tasmania, on the King Is. – transparent orange and yellow scheelite. On Sri Lanka, gem-quality yellowish-brown scheelite is extracted at placers, where its fragments reach 80 ct. In China, large crystals of scheelite were found at many deposits in the Guandong; Guizhou, Liaoning, Sichuan, Hunan and Jiangxi Prov. Near the Pingwu, Sichuan Prov., brownish-yellow crystals of scheelite reach the size of 15 cm.; and in the Hunan Prov., up to 10 cm. – at the Mang Yao mine; also at the Xihuashan mine, Jiangxi Prov. In Malaysia, at the Keramat Pulai mine, in the valley on the Kint River, crystals of scheelite reached the size of 20x14 cm. In Japan, in the Oyama region, they found crystals of scheelite up to 33 cm. in cross-section. In South Korea, to the southwest from Seoul, there are the deposits Tae Wha and Tong Wha with perfect crystals of scheelite in the form of pseudo octahedrons up to 18 cm. in size. They are white, black, brown, orange, red-brown, but the most interesting are violet-brown scheelites with purple tone. In the U.S.A., in Arizona, crystals of scheelite up to 15 cm. in size and 7 kg. in weight were found at the Cohen deposit, Cochise Co; and to 10 cm at the Tungsten Hill deposit. Their findings are also known in California, in San Bernardino Co.; in South Dakota and in Connecticut. In Brazil, in Minas Gerais State, large crystals of scheelite up to 12 cm. were extracted at the Morro Velho gold mine. In Mexico, gem-quality yellow and orange scheelite in crystals up to 20 cm. was extracted at the deposits Mitopilas and Santa Cruz, Sonora State; and in Bolivia – at the Condeaque deposit, Oruro Dept.

Synonyms. Scheelitic spar | Heavy stone | Trimontite | Tungsten, from Swedish “tung” – important.

Cut Gems. Because of its high level of dispersion in the faceted form, scheelite displays strong luster and play of color close to that of diamond. However, because of its low hardness it is of interest in collection purposes only. In the Smiths. Inst., Wash., there is faceted colorless scheelites from deposits of the California State, 18.7 ct. and 15.8 ct. in mass, and a golden-yellow scheelite from Mexico, 12.4 ct. in mass. In the Royal Ontario Museum, there is a colorless stone from California –14 ct., and in the AMNH, N.Y., a similar stone – 20.65 ct. In the Museum of Calgary, Canada, there is a scheelite from Nevada – 8.7 ct. On Sri Lanka, they found and cut in cabochon a star scheelite of yellowish-brown tone, 61.73 ct., with a four-radial star, formed with needle mineral inclusions.

Synthesis. In 1943, in the U.S.A., they manufactured colorless synthetic scheelite with the methods of stretching a crystal from melted mass and oriented crystallization. Because of admixtures, it can be yellow or brown, and with the admixture of neodymium – violet one. They made faceted stones from it up to 25 ct., which were sold to collectors as natural ones. With the same method, with the admixture of neodymium, they manufacture violet crystals of synthetic calcium tungstate, synthetic lanthanum tungstate, and synthetic sodium tungstate.

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