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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

STAUROLITE


STAUROLITE (Staurolith—Staurolite——тавролит) (Bergmann, T.O. 1792), from Gk. “stauros” – cross and “litos” – stone, after the shape of twin crystals, or cross stone.

Composition & Properties. Silicate – 4Al2[O|SiO4]·AlFe22+O3OH, subclass orthosilicates, monoclinic system. Hardness 7-7.5. Density 3.6-3.8. Glass luster, greasy one on chips. Perfect cleavage in two directions. Fragile. Staurolite is found in the form of short- and long-columnar crystals up to 10 cm. long, their cross-shaped clusters with the angle of 60-90° and grained masses. Color: yellowish-brown, reddish-brown, brown to black, more rarely red and dark blue. Non-transparent, weakly translucent at the edges of small crystals. Staurolite displays pleochroism from colorless to yellow, or from red to golden-yellow. A transparent red variety is called red sappare. Depending on admixtures they classify the following varieties: brown-red – nordmarkite with admixture of Mn2O3 up to 11.6%; black to blue – lusakite with the admixture of CoO up to 8.5%; xantholite – enriched with mineral admixtures of garnet, ilmenite, magnetite, rutile and micas; and yellowish-brownish – zincstaurolite with admixture of ZnO up to 7.4%. The last one is preferable for faceting because of its light color. It displays pleochroism from green to red up to yellow.

Deposits. Staurolite is a typical mineral of high-alumina metamorphic rocks. It is stable to weathering, it can be accumulated at placers. In Russia, it is found in significant volume on the Kola Penin., in micaceous schists of the Keivy Range, in the region of Semiostrovje and Shuururta Mt., where the size of separate crystals reached 20 cm. In Karelia, staurolite was discovered at the Khizovara deposit. Another region of wide development of staurolite schists is the South Urals, in the region from the Taganai Mt. to Uvil’da Lake, to the north-east from Zlatoust; and also the Svetlinskoye deposit, near Plast. In Siberia, findings of staurolite are known in Yakutia, in the region of Olekminsk; in the Western Pribaikalia the re is the Kholodnenskoye deposit, where they find zinc-containing staurolite; and on the Taymyr Penin. there is the Staurolite Mt.

In Europe, because cross stone is very popular among Catholics, its deposits are well researched. In Sweden, in the Värmland, near Nordmark, there is a deposit of brown-red nordmarkite. In Switzerland, they found transparent brown crystals of staurolite in the region of Saint Gottard Pass and at the deposits Alpe Sponda and Pizzo Forno, canton Ticino. In Austria, in the Styria, there is a similar deposit of staurolite – St Radegund; and in Italy – another one, in Southern Tyrol. In Romania, at the Sâliciua de Sus deposit, in garnet-containing micaceous schists, they found crystals of staurolite up to 15 cm. long. In Germany, staurolite was extracted near Aschaffenburg, Bavaria; and in France – at the Morbihan deposit, Brittany; and in Spain – in the Compostella, Prov. de Orense. In Greenland, crystals of gem-quality staurolite are called grenalite. In Zambia, 120 km. east from Lusaka, they discovered a deposit of jewelry-ornamental, cobalt-containing staurolite, which received the local name lusakite. In Namibia, large red-brown crystals of staurolite were extracted at the Gorob mine. Besides, layers of metamorphic schists with staurolite are widespread in Afghanistan, India, Madagascar and other countries. In the U.S.A., staurolite is very popular, too. Its deposits are exploited in many states, both western and eastern ones. In Massachusetts, fine crystals up to 10 cm. on Pearl Hill, Worcester Co. are known. From crystals of the Mineral Bluff deposit in Georgia they made faceted stones up to 1 ct. In Brazil, staurolite is extracted at the deposits Ardenella and Rubelita, Minas Gerais.

Synonyms. Bamlit, after the discovery location near Bamle, Norway | Fibrous chert | Magic cross | Stone cross | Lapis crucifer | Fibrolite, from Lat. “fiber” and Gk. “litos” – a stone, because of the fibrous texture of its aggregates | Prismatic garnet | Granatite | Black granatite | False jade | Lusakite, after the discovery location near Lusaka, Zambia | Nordmarkite, after the discovery location near Nordmarken, in the region of Oslo, Norway | Cruciate schorl | Brilliant spar | Staurotide, obs. | Cruciate stone | Lucky stone | St Andre’s stone, Fr. | Baseler Taufstein, Germ., syn. baptismal stone.

Cut Gems. Because of its cross shape, staurolite is also called magic stone. In Great Britain and France staurolite is especially popular, because they make rosaries from it. In the ancient times, in England, they believed that it was fallen from heavens. It is usually used without processing in jewelries and amulets. In Switzerland, staurolite is called Basel christening stone, because in Basel a cross from it was hanged on the neck of a baby during the christening. The surface of such crosses (they are up to 5 cm.) is just slightly lapped. Sometimes, non-transparent stones are cut in cabochon. The best samples of staurolite from the Swiss Alps and from Brazil were faceted. Such faceted stones were not more than 2 ct.; they were of interest for collection purposes only. In the Smiths. Inst., Wash., there is a faceted dark brown stone from Brazil 3 ct. in mass.

Legends. There is a legend, that staurolite was formed from tear of fairies, who mourned the death of Jesus Christ, that’s why it was called fairies stone. In Austria staurolite is supposed to be a stone of the Tyrol. In the U.S.A., it serves the official symbol of the Georgia State.

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