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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

CHAROITE


CHAROITE (Charoit—Charoite—„ароит) (Rogova V.P. et al., 1978), from Rus. “chary” – charms or magic, alluding to the impression that the mineral’s color and iridescence impart. Although, sometimes, they mention that it was called after the Chara River, 70 km. from the deposit, Yakutia, Russia.

Composition & Properties. Silicate – K(Na)5(Ca,Ba,Sr)8[(OH,F)|Si6O16|(Si6O15)2]•nH2O. subclass band silicate, monoclinic system. Hardness 5-6. Density 2.5-2.7. Glass luster, pearl to silk one in aggregates. Charoite is a mineral and a rock composed with it, which should call more correctly charoitite. This alkali rock was discovered in Russia, in the Murun massif between the rivers Chara and Tokko, near the border of Yakutia and the Irkutsk Region. At first, charoite was noticed they’re in 1949, but it was taked for lilac cummingtonite. In 1962, it was found at the same place but this time in significant quantities; its rock-forming mineral was classified as canasite. Soon, the deposit of this beautiful ornamental rock called Sirenyevyi Kamen’ (Lilac stone), was opened for work. But as a new mineral, charoite was described only in 1978. Individual samples of charoite are ultra thin thread-like crystals, which form needle, plate, twisted-fibrous, parallel-fibrous and radial-rayed aggregates, as well as cryptocrystalline masses. The length of plates of charoite aggregates reaches in some cases 22 cm. Mineral is non-transparent to translucent. Its color varies depending on the size of grains and rock texture. Fine-grained nephrite-charoite, also called red jade, is dark violet. Coarse-grained parquet charoite is silver-lilac with iridescence. Fibrous asbestos-charoite is snow-white. Parallel-fibrous aggregates of asbestos-charoite after polishing, sometimes, display the effect of cat’s-eye. Charoite display pleochroism from colorless to pink one. Violet color is linked with the admixture of manganese, brown tones – with iron (Fe3+). In ornamental material they estimate the color depth, silk play of color – chatoyancy and minimum quantity of mineral admixtures.

Deposits. The origin of charoite is connected with hydrothermal-metasomatic process at the contact of the Murun alkali massif. According the form of bedding, they classify columnar, layer, vein and schliere bodies of charoitite. This metasomatic rock in 40-100% consists of charoite and usually possesses inclusions of microcline, quartz, aegirine, miserite, pectolite, richterite and other minerals. The presence of ekanite admixture creates increased radioactive back-ground. In the content of charoitite, there is also tinaksite as yellow radial-rayed or sheaf-like aggregates, more rarely – as separate plate crystals up to 10-15 cm. long. In big carved produce such aggregates enrich ornamental properties of charoite (photo p. 28). Sheaf-like and star inclusions of dark green aegirine can be also very beautiful. As jewelry-ornamental material they use rock with the content of charoite from 95 to 30%. The best-quality vein of charoite was 100x80 m.2 in size and was tracked down to the depth of 30 m. The resource prognosis of the deposit is about 23,000 tons.

Quality improvement. To strengthen the color of charoite it is improved through gamma-rays irradiation. There is also information about the usage of the method of impregnation with organic dyes with the same purpose together with siliceous soles to strengthen the stone. Dark colored varieties of charoite are annealed to make them lighter in tone.

Cut Gems. When polished, charoite is extremely beautiful because of its chatoyant lilac hue with silk and pearl luster and various textures. These unique properties of the stone take the attention of stone-carvers and artists. At the same time, unfortunately, a significant amount of this rare stone goes to the manufacturing of cheap bijouterie, heavy vases, primitive and non-artistic jewelries and other articles. Charoite vases up to 28 cm. they cut out from whole blocks of stone. Sometimes, they use charoite even for coating in interiors. The office of “Aeroflot” in Paris is coated with it. Such uneconomical usage of this stone can lead to the repeating of the story with Ural malachite and rhodonite. Examples of usage of charoite in mosaics are more rational. In the Institute of Synthesis of Mineral Materials in Alexandrov, Vladimir Region, there is such a work of art – a tabletop with mosaic upper part, 2x1 m. in size, composed with different varieties of charoitite.

Similar Gemstones & Imitations. Charoite looks like sugilite. As material for artificial imitation of charoite, they use pressed barium-phosphate with bonding agents, as well as plastics.

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