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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

ANDALUSITE, GROUP: ANDALUSITE, KYANITE, SILLIMANITE


ANDALUSITE group (Andalusit—Andalousite—јндалузит) (Delamétherie, J.C. 1798), after its discovery location in the Andalucía Prov., Spain. Here we also describe identical in the composition kyanite and sillimanite.

Composition & Properties. Silicate – Al[6]Al[5][O|SiO4], subclass orthosilicates, orthorhombic system. Hardness 6.5-7.5. Density 3.1-3.2. Glass luster. Cleavage in one-two directions. Fragile. Andalusite is found as prismatic crystals of the columnar shape, which can reach a significant size. Besides, its columnar and grained aggregates are known. Transparent to non-transparent. Color: in its pure form – colorless, depending on the composition of properties – gray, pink, olive-green and violet. Iron oxides colored andalusite yellow along cracks. Its own color depends on the admixtures of iron, manganese, chromium, and also on micro inclusions of carbon small parts, and magnetite. Besides, as inclusions, there can be apatite, biotite, rutile and other minerals. In manganandalusite the composition of Mn2O3 is up to 7%, and Fe2O3 – up to 5%. In dark green manganandalusite – viridine pleochroism is displayed obviously – from green to brownish and red. This variety is called sometimes alexandrite-like andalusite, although it has no ability to change its color in artificial light. Andalusite cat’s-eye is observed in cabochons because of the presence of hollow tubes of growing in them – channels and inclusions, oriented along the long axis of crystals. They find not rarely a figure of black cross in basal slabs of half-transparent reddish-brown crystals of andalusite, because of inclusions of coaly or clay substance. This variety has the trade name chiastolite, or crucite and it is characterized with less hardness (5-5.5).

Deposits. Andalusite is more or less widespread mineral, which is formed mainly in the process of contact metamorphism and metasomatism. Because of its stability to weathering, it is accumulated at placers, from which the main weight of gem-quality material is extracted. In Russia, in Kabardino-Balkaria, along the Baxan River, they found veins with crystals of andalusite up to 7 cm. long. In the Middle Urals, in the region of the village of Yuzhakova, they found crystals of andalusite 10x0.5 cm. in size, green in the center and pink at the edges. In the South Urals, in the Plast town area, its pale pink crystals up to 9 cm. long were extracted at the Svetlinskoye deposit; and in the Ilmeny Mts. their size in pegmatites reached 20-60 cm. In East Transbaikalia, near the village of Mankovo, Nerchinskiy Dist., there were findings of crystals of red-brownish chiastolite up to 4 cm. long, and along the Argun’ River they found yellow-gray crystals of andalusite. In Azerbaijan, crystals of andalusite were found at the Paragachay deposit. In Kazakhstan, andalusite is found at the Semiz Bugy deposit. In Uzbekistan, at the Nuratau Ridge pink andalusite in crystals up to 20 cm. long was extracted from pegmatites in the upper reaches of the Lyailik River. In Kyrgyzstan, it is known in the Turkestan Ridge, in pegmatites of the Kyrk Bulak deposit, and at the extension of this range in North Tadzhikistan. In the West Pamirs Mts., crystals of half-transparent brownish-pink andalusite up to 1.5x8 cm. in size were found in miarolitic cavity of oligoclase pegmatites in the region of the Kukh-i-Lal deposit, as well as at the Namangut deposit.

In Austria, in Tyrol, there is the Lisenz deposit of andalusite; and in Carinthia they found crystals of red andalusite up to 3x1 cm. in size at the Kreuzeck deposit. The biggest from them was 13.5x3 cm. in size. In Switzerland, in the Pischa Mt., near Grisons (Graubünden), crystals of andalusite reached 20 cm. long. In Czech Rep., large crystals to 50 cm. form in granite pegmatites at Dolní Bory, Moravia. In Belgium, in the region of Salmchâteau, they discovered viridine in the shape of crystals with pleochroism from emerald-green to golden-yellow, available for faceting. In France, polychromatic crystals of chiastolite were found at the Sal de Roan deposit in Brittany. In Spain, chiastolite in significant quantities was found in metamorphic rocks of West Asturias. In Algeria, the Bone deposit of chiastolite is situated near Bon Ganif, Constantine Prov. In Southern Australia, at the Bimbowrie deposit, near the Howden Mt., they discovered gem-quality chiastolite with the fern-like pattern in slabs, in the shape of twin crystals up to 4 cm. long. It is so called howdenite. There, they extracted also red-violet andalusite. In China, in the Henan Prov., the andalusite and chiastolite are processed for jewelry purposes in the shape of slabs up to 6 cm. in cross-section. In Myanmar and on Sri Lanka, gem-quality green andalusite in crystals up to 3 cm. is extracted at placers. In the U.S.A., wonderful crystals of andalusite up to 15 cm. long come to the market from New Hampshire and California. In California, in pegmatite vein of the Batista Canyon deposit, they found a crystal of andalusite 61x15.24 cm. in size; in Chowchilla locality – andalusite – chiastolite. In Massachusetts, near South Lancaster, there is a deposit of the best chiastolite. It is represented with large cigar-shaped crystals with typical cross-like pattern in basal slabs on the white, yellow, brown and red background. In Virginia, in the Campbell Co., there is a deposit of andalusite with crystals up to 50 cm. long. In Canada, in pegmatite and quartz veins of the North-Western Territories, they find crystals of pale violet and pink andalusite, up to 10 cm. long, and in Québec they discovered viridine. In Brazil the main mass of andalusite available for faceting is extracted at placers. In the Espírito Santo State, at the Santa Teresa deposit, from gem-quality crystals of polychromatic green-rose and yellow-rose andalusite they received faceted stones up to 20 ct., more rarely – up to 75 ct. Transparent viridine was extracted in Minas Gerais State, near Minas Novas, at the Santa Maria deposit, and also in the northwestern part of the state, at the Maricota deposit. On the Jequitinhonha River they extracted brownish viridine at placers. In Bolivia and Chile, there were also findings of gem-quality andalusite crystals.

Synonyms. Pseudo-andalusite | Manganandalusite | Apyre, obs. | Chizeuilite (chezeulite), twinned cros-sformed, after the Chizeile deposit, France | Couseranit, after the discovery location near Couseran, France | Rose garnet | Micaphyllit (micafilit, micaphilit), from Lat. “micare” – to glisten and Gk. “phillon” – a leaf, because of its cleavage | Hard spar | Stanzait, after the discovery location near Stancän, Bavaria, Germany | Stealit, twinned cross-formed.

Chiastolite, from Gk. “hiastos” – placed in diagonal, because a cross of coal inclusions is observed in basal slabs – crucite (crucilith, crusite), from “crucial”, cross-shaped | Holzspath, Germ. | Howdenite, after the discovery location near the Howden Mt. in South Australia | Krestovik, Old Russ., or cross stone | Macle, from Lat. “macula” – a spot, because of coaly inclusions | Basaltique macle | Hyalin macle | Maltesite, because of the similarity of a cross-shaped pattern with the Maltese cross | Maranite, after the discovery location near Sierra de Mare, Portugal | Hollow stone.

Manganandalusite – Gosseletite (gosselit) | Viridine, from Lat. “viridis” – green, discr.

Treatment. Transparent crystals of andalusite are faceted in brilliant and step patterns, especially those with zonal coloring: green or pink in the center and brown at the edges. Usually their weight is not more than 5 ct. Red hue is observed in the best way in the direction of the prism edges, it should be taken into account during the process of faceting. Green hue can be transferred into pink with annealing. Rare and valuable cabochons are those, which display the effect of cat’s-eye. The biggest faceted stones from Brazil are exhibited in the Smiths. Inst., Wash.: a brown one, 28.3 ct. and a green-brown one, 13.5 ct.; and in the Museum Hist. Nat., Paris, another sample, 40 ct. In private collections there are faceted stones up to 100 ct. Flat insets from chiastolite-stealit with the pattern of a black cross on the white background are very popular among clergymen for rosary; and pilgrims use them as amulets.

Similarity. Andalusite looks like vesuvianite, smoky quartz, sinhalite, titanite, tourmaline and chrysoberyl.

Kyanite (Kyanit—Cyanite— ианит) (Werner, A.G. 1789), from Gk. “kyanos” – blue, is alluding to its most common color. Silicate – Al[6]Al[6][O|SiO4], triclinic system. Hardness 4.5 – along the long axis, 7 – across the long axis. Density 3.6. Glass luster. Perfect cleavage. Fragile. Kyanite, or disthene is found in the shape of oblong lamellar crystals, twisted-fibrous and radial-rayed aggregates kyanite suns. Transparent to weakly translucent. Color: pale blue, violet-blue, bluish-green, emerald-green, yellow to almost colorless. White kyanite, sometimes transparent, and colorless one have the trade name rhatizit. Distribution of color in crystals is often uneven: zonal, spotty with concentration in the center. Obvious pleochroism is typical – from colorless to dark blue. The nature of blue color of kyanite is linked with the admixture of titanium, green chrome-disthene – of chromium, yellow and yellow-green – of iron. Besides, microinclusions of graphite and magnetite lead to gray and black color. Brownish hue depends on inclusions of hematite. Kyanite often contains inclusions of quartz, rutile, garnet and other minerals. Sometimes, in cabochons of kyanite they observe the effect of cat’s-eye and asterism because of inclusions of ilmenite, and in chromium-containing kyanite – the alexandrite effect.

Deposits. Kyanite is a typical mineral of metamorphic rocks, however it is found also in kimberlites, pegmatites and in hydrothermal and alpine veins, too. In Russia, on the Kola Penin., in West Keivy, there is a deposit of kyanite in the Serpovidnyi Range with crystals up to 1 m. long. In small quantities they find their gem-quality material of blue and green color. In Karelia more perspective in this sense is the Khizovara deposit of kyanite. Their light blue kyanite-containing schists with green inclusions of fuchsite are used as an ornamental stone for manufacturing of cabochons, brooches and balls. In the South Urals, at placers on the Kamenka and Sanarka Rivers, they extracted cornflower-blue and violet crystals of kyanite up to 4 cm. long. They were faceted and sold under the Russian trade names ovsyanka or kaslinite. There, near Plast town, in quartz-sericite schists of the Borisovskoye deposit they find well-formed crystals of kyanite up to 20 cm. long. In the Irkutsk Region, in pegmatites of the Mamskiy Dist., findings of large crystals of kyanite are known. In Yakutia, on Aldan, at the Chainyt deposit kyanite-corundum rocks can contain gem-quality chrome-kyanite.

In Romania and Slovakia, in metamorphic rocks they found crystals of kyanite up to 20 cm. long. In Switzerland, Italy and Austria, in alpine veins, they found transparent crystals of kyanite up to 10 cm. long. In F.Y.R.O. Macedonia, gem-quality kyanite up to 50 cm. is found in area Prilep. In Italy, in Tyrol, at the Val du Vizze deposit, they find collection white kyanite. In Kenya, at the Machakos deposit, near Sultan Hamud, from transparent crystals of blue and green kyanite they made faceted stones up to 15 ct. In Tanzania, emerald-green kyanite is extracted at placers on the Umba River. In Namibia, large light blue crystals of kyanite were found at the Gorooab mine. In Australia, in the Northern Territory, in the area Harts Range they find greenish-blue kyanite in crystals up to 30 cm. long with transparent parts up to 10 cm.

Among the other countries, we should mention the largest in the world deposits of kyanite in India, in the Bihar State. They are observed as a band 70x10 km. long to the Orissa State. In the Bihar State, at the Lapse Buru deposit they find gem-quality blue and greenish-blue crystals with asterism and kyanite cat’s-eye. The states of Punjab and of Jammu and Kashmir (disputed area) are another region in India, where gem-quality kyanite has been extracted since the ancient times. In the 17th cent., it was sent to Russia as a cheap imitation of sapphire under the trade name baus. There are also other large deposits of kyanite in India: Khammam, Bhandara, Sidhbum. On Sri Lanka, in Myanmar, Nepal and Korea, kyanite is extracted at placers together with other gemstones.

In the U.S.A., in pegmatite veins Selo Mine, North Carolina, the size of crystals of kyanite reaches 40 cm. From this place gem-quality material with the output of faceted stones up to 6.5 ct. is registered; and at the Balsam Gap deposit – faceted stones are up to 9.58 ct. In the states of Montana and Georgia, they described findings of crystals of kyanite up to 5 cm. long, available for faceting. Some of them display the effect of cat’s-eye in cabochons. In Brazil, fine columnar crystals of kyanite up to 15 cm. in length were extracted at the Barra da Salina deposit, Minas Gerais. At placers of the region of Capelinha Malacacheta, the size of light blue crystals of kyanite reaches 30 cm. They made from them faceted stones up to 10-25 ct. In Chile, there are also deposits of kyanite.

Synonyms. Baus (bogus), Old Russ., after Jeremy Baus, an English gemstone merchant in Moscow, in the epoch of Ivan the Terrible; also a common name for cheap blue stone in Russia | Azul beryl | Leaf-like beryl | Chrome-kyanite, after its color | Cianite, obs. | Disthene, from Gk. “dis” – in two ways and “stenos” – hard, after its hardness | Kaslinite, after the discovery location near Kasli, at the Urals, Russia | Nilum, from Sanscr. “nila” – light blue | Ovsyanka, as an oblong pebble, Old Russ. | Rhatizit (rhadezite), after the name of the Roman Prov. Rhatia, now Tyrol, Austria | Sapparite (sappare), Scotch, from sapphire | Talc schorl | Distene prismatic spar | Sapphire spar | Blue talc | Xantholite from Gk. “xanthos” – yellow and “litos” – a stone | Zyanit..

Treatment. Gem-quality kyanite is relatively rare and difficult in processing because of anisotropy of hardness and perfect cleavage. However, they make stones not only of step but also of brilliant pattern of faceting. In the Smiths. Inst., Wash., there are faceted stones from Brazil of blue and green color, 10.7 and 9.1 ct. in mass; and also a blue stone from Tanzania 4.9 ct. In the Museum Calgary, Canada, there are faceted African stones 14 and 8.5 ct. Translucent cabochons up to 10 ct. are used as imitation of Indian sapphire.

Similarity. In faceted form kyanite can be taken for aquamarine, benitoite, dumortierite, cordierite, and sapphire.

Sillimanite (Sillimanit—Sillimanite——иллиманит) (Bowen, G.T. 1824), after Benjamin Silliman (1779-1864), Professor of Chemistry and Geology, Yale University, New Haven, Connecticut, the U.S.A. Silicate – Al[6]Al[4][O|SiO4], orthorhombic system. Hardness 6.5-7.5. Density 3.2-3.3. Glass luster, silk one in fibrous aggregates. Perfect cleavage in one direction. Usually, it is represented with radial-rayed and twisted-fibrous aggregates of fibrolite. Rarely they find columnar and needle crystals up to 10x0.5 cm. in size, hardly available for faceting. Color: light bluish to colorless, gray, light brownish, yellow, brown and pale green in aggregates. Its color depends on the admixtures of iron, chromium, and titanium, replacing aluminium in the crystalline lattice of the mineral. Light bluish-green, pale blue, violet-blue fibrous fibrolite displays the non-clear effect of cat’s-eye and strong pleochroism in cabochons, mainly because of the transformation of thickness of color. Sillimanite often forms inclusions in – sillimanite hair stone, and in noble spinel inclusions of sillimanite lead to asterism.

Deposits. Sillimanite is formed in the process of contact metasomatism in mica-schists and gneisses. In Russia gem-quality varieties of sillimanite were not found except separate findings in the South Urals. There, at the Svetlinskoye deposit, in contacts with quartz veins fibrolite was formed, and in crystals of rock crystal inclusions of sillimanite up to 7 cm. long were not rare, they formed quartz hair stone. In Europe, sillimanite was discovered in Germany – in Bavaria, near Bodenmais; in Czech Rep. – in Moravia; in Austria – in Tyrol. Among the other countries, colorless, light bluish sillimanite available for faceting was found in Kenya and Tanzania, at placers on the Umba River. In Myanmar (Burma) gem-quality violet-blue sillimanite in crystals up to 5 cm. was extracted as additional material with other gemstones at placers in the region of Mogok. At placers of Sri Lanka they find light blue fibrolite, which display chatoyancy and fibrolite cat’s-eye in cabochons. In India, in the Assam State, there are the largest deposits of sillimanite in the shape of lenses and pockets in schists, including those with sillimanite cat’s-eye at the Kazi Hills deposit; in the Bihär State – the Pipra deposit; and also in the Orissa State. In the U.S.A., placers, where they extract sillimanite cat’s-eye, are situated in Idaho, in the valley of the Clearwater River; in brown crystals up to 10 cm. in Oconee Co. South Carolina; and in fine crystals at the Culsagee mine, Macon Co., North Carolina.

Synonyms. Bournonite | Bucholzit, from deposit Buchholz in Carinthia, Austria | Monroelite (monrolite), after the discovery location near Monroe, the U.S.A. | Brilliant spar.

Treatment. Sillimanite is difficult in processing as kyanite. Massive variety of brownish and green fibrolite resembles jade. They make from it cabochons with the effect of cat’s-eye up to 20 ct. Rare transparent pale blue crystals are faceted for collection purposes. They look like pale variety of cordieritewater sapphire. To receive the maximum intensity of their color, a table facet of a stone should be oriented in the right angle to the long axis of a crystal. In the British Museum, London, there is the biggest faceted sillimanites: light blue fibrolite 35 ct. and violet-blue one – 19.84 ct. In the Smiths. Inst., Wash., there is a cabochon of fibrolite cat’s-eye 5.9 ct.

Similarity. In faceted form blue sillimanite looks like cordierite and sapphire, and pale one looks like euclase.

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