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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

DANBURITE


DANBURITE (Danburit—Danburite—ƒанбурит) (Shepard, C.U. 1839), after its discovery location at Danbury, Fairfield Co., Connecticut, U.S.A.

Composition & Properties. Silicate – Ca[B2Si2O8], subclass framework silicate, orthorhombic system. Hardness 7-7.5. Density 3.0. Glass luster, greasy one, diamond one on polished faces. Fragile. Danburite is found in the form of long-columnar crystals of orthorhombic profile, resembling topaz, but without its perfect cleavage. Transparent to translucent. Color: colorless, white, rose, yellow, brown, gray. Sometimes color is zonal with thickening at the edges to brown tone. It forms massive radial-rayed, columnar and grained aggregates. It is found also in the form of nodules up to 3 cm. in cross-section and crystals covered with solid carbonate coat. Sometimes, danburite contains inclusions of needles of tourmaline and flakes of chlorite. Such transparent danburite hair stones are called in the U.S.A. bementite.

Deposits. It is formed in pegmatites, in the conditions of metasomatism – in greisens, in the process of contact metamorphism – in skarns and endogenous salt domes. In Russia, on the Taymyr Penin., in a salt dome of the Belaya Mt. deposit of fluorite, they extracted bluish-gray danburite crystals up to 5 cm. long, available for faceting, as additional material. In oligoclase pegmatites of Central Transbaikalia, in the Malkhan Ridge, in the danburite vein, they found both colorless and orange danburite crystals up to 15 cm. long with segments of gem-quality. In the Primorskiy Region, at the Dal’negorskoye (form. Tetyukhe) deposit, in enormous cavities in skarns perfect crystals of transparent light yellow danburite up to 50x10 cm. was extract. In the Central Siberian Geological Museum in Novosibirsk, there is one of the biggest druses of danburite, 200 kg. in mass, with crystals up to 30 cm. In the Magadan Region, at the Canyon deposit, in the region of the settlement of Seimchan, the size of its crystals reached 2 cm. In Tadzhikistan, pale yellow danburite together with axinite is found at the Ak Arkhar deposit, Pamirs Mts. In the East Pamirs Mts., in the region of Murghob, it was discovered in pegmatites of the Kukurt deposit, not far from Rangkul’ Lake, where it is represented with orange crystals up to 8x2.5 cm. in size. Transparent segments in them are not more than 4x1.5 cm. In the light its color is not stable; it becomes light yellow. In crystals, perpendicular to the long axis, channels are seen, which can produce the effect of cat’s-eye cabochon. In Turkmenistan, findings of danburite crystal are known at the Gaurdak deposit. In Austria, and Switzerland it is found in alpine veins in the form of perfect light yellow crystals up to 3 cm. long.

On Madagascar, at the deposits Sakhasonyo, Makharitra and Anjanabonoina, in the region of Antsirabe, they discovered the biggest crystals of yellow and yellow-brown danburite. They were more than 50 cm. long; from their transparent segments faceted stones up to 50 ct. were made. At placers of Myanmar (Burma), in the region of Mogok, they extracted gem-quality colorless and yellow danburite crystals up to 5 cm. In Japan, in hydrothermal veins, its colorless crystals reached 9 cm. at the Obira deposit, Oita Pref.; and green opaque crystals up to 24 cm. at the Toroku mine, Miyazaki Pref. In the U.S.A., besides the first finding near the city of Danbury, Connecticut, in 1839. In New York, beautiful crystals at the Russell deposit were found; and in California golden brown crystals up to 10 cm. – at the Little Three mine, San Diego Co. In Mexico, in Baja California, colorless and rose danburite is extracted in significant volume at the deposits Minala Serene and Zimpan, also in San Luis Potosí State – at the deposits San Sebastian and La Aurora, near Charkas. There are gem-quality colorless, yellow and light rose crystals reached 16 cm. long. They made faceted stones up to 38.67 ct. from them. Adruse of danburite from the La Aurora mine was 25 cm. wide; at the Tucson jewelry show, the U.S.A., in 1997 it was evaluated in $1,800. In Bolivia, at the Chapare deposit, Cochabamba Dept., findings of danburite up to 4 cm. are known.

Quality improvement. Danburite is nor very popular in jewelry as a gemstone because of its pale color. The method of gamma-irradiation gives the possibility to reveal or strengthen its color to orange-yellow and brown. Danburite from the Dal’negorskoye deposit becomes amber-yellow with clear zones – it displays alternating layers of different intensity of tone; or smoky zones. Irradiation color is stable under the room temperature, but it completely disappears under annealing. Recent years, they practice quality improvement of danburite with the method of evaporation with gold to make light blue film with iridescence on the surface of colorless crystals.

Synonyms. Bementite, after the Amer. collector C. Bement | Mexican diamond.

Treatment. Danburite is faceted mainly for collection purposes. The brilliant pattern of faceting is preferred to use the advantages of its exclusive transparency. The biggest faceted stone was made from material of Myanmar placers – it was yellowish-rose, faceted with the step pattern, 138.61 ct., and 3.18x2.96x1.52 cm. in size. Now, it is exhibited in the British Museum, London. In the Museum of Ottawa, Canada, there is a stone from Madagascar of the fantasy pattern of faceting, orange color, and 86.53 ct. In one of private collections there is a faceted danburite of peach color, it is from Myanmar, 20 ct.; and in the Smiths. Inst., Wash. there is a yellow stone from Madagascar – 18.4 ct. and a colorless one from Japan – 7.9 ct.

Similarity. Danburite looks not only like topaz, but also like apatite, hambergite, datolite, phenakite and citrine.

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