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Russian Gemstones Encyclopedia

Vladimir Bukanov. Russian Gemstones Encyclopedia

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AXINITE


AXINITE group (Axinit—Axinite—јксинит) (Haüy, R.-J. 1797). A group name from Gk. “axine” – axe, after the typical shape of its crystals.

Composition & Properties. Borosilicate. Triclinic system. Hardness 6.5-7. Density 3.2-3.3. Glass luster. Fragile. Cleavage in one direction. Minerals of the axinite group are characterized with alternating composition, because they form rows of constant miscibility among themselves. A ferrous member of the row is brownish-violet ferro-axinite – Ca2Fe2+Al2B[4][O|OH|(Si2O7)2] , which is the mostly widespread. Magnesio-axinite – Ca2MgAl2B[4][O|OH|(Si2O7)2] is a magnesia member of the row, it is light blue. Manganaxinite – Ca2Mn2+Al2B[4][O|OH|(Si2O7)2] is manganese-containing, greenish-yellow to brownish and emerald-green. Tinzenite – (Ca2Mn)2Mn2+Al2B[4][O|OH|(Si2O7)2] is extreme member of the row of manganaxinites, it is orange-yellow to red. Only in 1953, after more precise description of its composition, it was classified as one of the group of axinite. For all the varieties of this group flattened, wedge-shaped crystals are typical. Axinite can be found alas well as grained masses. Transparent to translucent, it often possesses inclusions of actinolite, epidote and other minerals. Its color depends on the presence of iron and manganese in its composition. Sometimes, its color is not stable and is weakened after long staying in light. Axinite is characterized with strong pleochroism: from olive-green to violet to blue and brownish. In magnesio-axinite the alexandrite effect is observed – it is pale blue in the day-light and pale violet in the electric light.

Deposits. Axinite is a typical mineral of pegmatites, metasomatic and metamorphic formations – hornfels, skarns, and alpine veins. In Russia, gem-quality axinite is found rarely, mainly in alpine veins. On the Kola Penin. they extracted its non-transparent collection crystals as additional material at the Pechenga copper-nickel deposit. On the eastern slope of the Subpolar Urals Mts., axinite was extracted in significant quantities at the Puiva deposit of rock crystal, where large pockets with axinite were opened. The size of separate flattened crystals reached their 22 cm. However, transparent crystals with thread-like inclusions of actinolite were not more than 12 cm. long. Not far from Puiva there is the Khus’oika deposit with less in size pockets of axinite and low output of gem-quality material. In the upper reaches of the Man’ya River axinite was found at the Man’ya Nell deposit of rock crystal. Besides, on the eastern slope of the Urals, near the Vysokaya Mt., findings of axinite were known in the upper reaches of the Khobe-Yu River. They found mainly half-transparent crystals up to 5 cm. there. On the western slope of the Subpolar Urals Mts., findings of non-transparent crystals of axinite in paragenesis with adularia were registered at the Pogranichnoye deposit, in the source of the Kozhim River. In the Middle Urals, axinite was discovered near Yekaterinburg, by the village of Palkino, and also at the Pervoural’skoye deposit. In the South Urals, findings of its crystals were described at the Tungatarovskoye deposit of rhodonite and at the Berkutova Mt., by the village of Polyakovka. Among rhodonite they discovered manganese-containing axinite – severginite. In Primorskiy Region perfect crystals of manganaxinites, up to 25 cm. in size, were extracted at the Dal’negorskoye deposit. In the eastern part of the Chukchi Penin., on the Daurkina Penin., well-formed crystals of axinite were found near the settlement of Chegitun; and at the Iunchon River.. In the Magadan Region axinite was discovered at the Canyon deposit, near the settlement of Seimchan. In Tadzhikistan, axinite was found at the Ak Arkhar deposit in the Pamirs Mts. In South Kyrgyzstan, axinite was discovered at the deposits Akjilga and Chalkuyruk, near Osh.

In Poland, at the Strzegom deposit, the Lower Silesia, found crystals manganaxinite. In France, gem-quality manganaxinites in crystals up to 15 cm. in size was discovered in alpine veins at the St Christophe deposit, Iséré Dept.; and in the Pyrenees it was discovered at the Cape d’Espade deposit. In alpine veins of Switzerland, at the Le Catoqne deposit, Wallis canton, crystals of axinite reached 17 cm. in cross-section; in the Alp Parsettens, Graubünden, they found orange-yellow to red tinzenite; and axinite is represented with beautiful druses at the Prosa deposit. In Germany, at the Radautal deposit, Harz Mts., occur at first greenish-yellow to brownish manganaxinite. In Tanzania, lilac-blue gem-quality magnesio-axinite with the alexandrite effect in crystals up to 5 cm. at Merelani Hill, near Arusha, was extract. There is information of additional extraction of transparent yellow, brown and violet axinite at placers of Sri Lanka. In India, in the Jammu and Kashmir State (disputed area), crystals of axinite up to 10 cm. at Alchori, Shigar Valley, were found, also as at the Khaploo deposit, near Skardu. In Japan, on the Kyüshü Is., at the Toroku mine, Miyazaki Pref., they found light bluish axinite in crystals up to 10 cm.; and at the Obira mine, Öita Pref., its crystals up to 10 cm. are of collection significance only. In Australia, ferro-axinite crystals up to 4 cm. at the Colebrook Hill mine, on Tasmania Is., are extracted. In New Zealand, at Akatore Creek, South Is. tinzenite is known.

In Canada, at the Gray Cloud Claim deposit, Yukon, brown-green crystals of axinite were found. In the U.S.A., in Arizona, they discovered emerald-green crystals of gem-quality manganaxinite. In California, gem-quality dark violet ferro-axinite up to 8 cm. occur at Coarse Gold, Madera Co.; and at the New Melones Dam deposit, Calavares Co., also near Fallbrook, San Diego Co. In Nevada findings of axinite crystals up to 12 cm. are known. In Mexico, at the mines La Olivia and Los Gavilanes, Baja California, transparent crystals of axinite up to 10 cm. were extracted. At the La Olivia mine, from crystals of axinite they made faceted stones up to 23.6 ct. In Brazil, collection crystals of ferro-axinite up to 22 cm. at Brumado deposit, Bahia, were found.

Synonyms. Afterschörl, Germ. | Hyalite | Yanolite (janolite), violet, obs. | Oisanite, after the discovery location in Bourg d’Oisans, France | Glassy schorl | Lentiform schorl | Violet schorl | Severginite, after the Russ. mineralogist V.M. Severgin (1765-1826) | Glassy stone | Thuma stone | Thumite, after the discovery location near Thuma, Saxony, Germany | Tinzenite, after the discovery location near Tinzen, Switzerland.

Treatment. Axinite in transparent crystals is rare; because of inclusions faceted stones are rarely more than 5 ct. Faceting is usually in the brilliant pattern. In the Smiths. Inst., Wash., there is a faceted axinite 23.6 ct. from Mexico, of Baja California State. In the Geol. Museum, London, there is a faceted tinzenite, 0.78 ct.

Similarity. Faceted axinite looks like andalusite, titanite, baryte and smoky quartz.

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