Russian Gemstones Encyclopedia

Vladimir Bukanov. Russian Gemstones Encyclopedia



CANCRINITE group (Cancrinit—Cancrinite—Канкринит) (Rosé, G. 1839), after the Count Georg Cancrin (Egor Frantsevich Kankrin) (1774-1845), Russ. Minister of Finance, 1823-1844. Here also vishnevite is described, which forms a row of constant miscibility with cancrinite.

Composition & Properties. Silicate – (Na,Ca,)8[(CO3,SO4)2|(AlSiO4)6]•2H2O, subclass framework silicate. Hexagonal system. Hardness 5-6. Density 2.4-2.5. Glass luster, pearl one on cleavage planes. Cleavage in one direction. Fragile. Cancrinite is found in the form of columnar crystals, but more often as massive grained aggregates. Color: colorless, yellow, orange, pink, red, greenish, pale-violet to deep blue. Transparent to translucent. Inclusions of hematite produce aventurescence in cancrinite sunstone. Because of this and of its bright color, it is of interest as jewelry-ornamental rough material. Cancrinite looks like nepheline.

Deposits. Cancrinite is linked mainly with pegmatites in alkali massifs and at contacts with them. In Russia, on the Kola Penin., in Khibiny, in the Nyorkpakhk Mt., they found rather large crystals of cancrinite. In carbonatites of the Kovdor deposit cancrinite is represented with half-transparent yellow veins up to 5 cm. thick. For the first time, it was discovered in pegmatites of the Ilmeny Mts., in the Urals. They found crystals of cancrinite up to 6 cm. long there, and also accumulations of its complete masses of yellow, lilac and light pink color, including those with aventurescence. In Siberia, findings of cancrinite are known in the East Sayan Mts., at the Bogotolskoye deposit. In Tyva Rep., crystals of cancrinite reached 1 m. long in the massif Dakhu Unur, Sangilen Ridge. In South Greenland, in Kagsit (Qassit) Fjord, in dikes of nepheline syenites, they found blue cancrinite of ornamental quality. In Canada, at the Bancroft deposit, Ontario Prov., they extract the best ornamental cancrinite of bright orange and lemon-yellow color. In the U.S.A., rose-red cancrinite was discovered in Colorado, at the Iron Hill deposit, and in Maine State, at the Connebeck deposit. Findings of colored cancrinite are known also in Norway, Finland and Romania. In Africa, its deposits are situated in Congo (Kinshasa), Angola, Uganda and Kenya. As an ornamental stone, cancrinite was extracted in China and India.

Transparent segments of crystals, available for faceting, are rarely found, that’s why faceted stones are not more than 1-2 ct. Massive cancrinite is cut mainly in cabochons and balls. The biggest cabochon from the material from Greenland was 57 ct.

Vishnevite (Vishnevit—Vishnevite—Вишневит) (Belyankin, D.S. 1931), after its discovery locality, at the Vishnevye Mts., South Urals, Russia. Silicate – (Na,K)6[(SO4|(H2O)2|(AlSiO4)6], hexagonal system. Hardness 5. Density 2.3. Glass luster. Cleavage in one direction. Fragile. In its composition, a form of occurrence and conditions of its genesis vishnevite is close to cancrinite, with which it forms an isomorphic row. It differs from cancrinite with the presence in its composition the anion SO4. Color: yellow, orange-yellow, bluish and white. Transparent to translucent. It is found in alkali magmatic rocks and in contacts with them. At first vishnevite was discovered in Russia, in the South Urals. Its massive ornamental variety of light blue to blue hue was extracted at the Kurochkin Log deposit, in the Vishnevye Mts. In Kyrgyzstan, in the Alayskiy Range, in the massifs Zardalek, Urusai and Chikindy, findings of vishnevite in fluorite and pegmatite veins were registered. In Great Britain, vishnevite is known in Scotland, at the Loch Borolan deposit. In the north-eastern part of Finland, not far from the Russian border, massive vishnevite up to 15 cm. at the Livaara deposit, near Kuusamo, was discovered. In Tanzania, it was discovered at the volcano Ol Doinyo Lengai, to the northwest from Arusha. In Guinea, on the Îles de Los (Los Iss.), vishnevite is called losite. In the U.S.A. vishnevite was extracted in Colorado, at the deposits Iron Hill and Beaver Creek, Gunnison Co. It was cut in cabochons and beads.)