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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

KAOLINITE, GROUP: KAOLINITE, ALLOPHANE, DICKITE, HALLOYSITE, GIBBSITE


KAOLINITE group (Kaolinit—Kaolinite—Каолинит) (Johnson, S.W. 1867), from the Chinese Kau-Ling, “high ridge” – the name of the hill near Jauchau-Fu, Jiangxi Prov., China, where the mineral was found. Here also minerals of the kaolinite group are described: allophane, dickite, halloysite and gibbsite rocks composed with kaolinite and ceramic made from it.

Composition & Properties. Silicate – Al4[(OH)8|Si4O10], subclass lamellar, triclinic system. Hardness 2-2.5. Density 2.6. Dull luster in aggregates. Hygroscopic. In its pure form kaolinite is white, ferrous kaolinite is yellow-brown to brownish. In the presence of allophane and Cr2O3 (up to 4%) it is green and is called miloschite. Kaolinite and minerals of its group are often found as inclusions in turquoise, opal and semi-opal. The size of separate fragments of kaolinite is microscopic, its crystals up to 2 cm. in cross-section were found as exclusions. Their color depends mainly on admixtures. Broad isomorphism is typical for minerals of this group. Kaolinite and minerals of its group are not gemstones, but they are represented in the composition of gemstones. Kaolinite and minerals of its group are formed in the process of weathering and transformations of feldspars in the rocks like granite, and later they are concentrated in sedimentary layers. Their aggregates like porcelain clay, stone brain or porcellanite are non-transparent. Kaolinite clay with the admixture of halloysite – keffekeilite is used for manufacturing of small decorative produce and pipes. Rose clay – rhodalite from the region of Antrim, Northern Ireland, Great Britain, is colored with Iron oxides; it is used for manufacturing of small souvenirs and fancy produce. Massive lavender-blue mixture of kaolinite with quartz, micas and limonite is called teratolith. Mixture of kaolinite, dickite, and quartz with cinnabar is a high valued ornamental stone in China. It is called chicken blood color stone, chicken blood stone or balin. This rock is extracted in Inner Mongolia and also in the Shanxi Prov., near Siang. The kaolin Kau Ling deposit in the Jiangxi Prov., has been exploited since the deepest antiquity. This Chinese clay was the first rough material for manufacturing of porcelain. In France, similar deposits are situated in the region of Limoges, Haute-Vienne Dept., where they produce Sevrian porcelain. In the Ukraine, the Poloshkovskoye deposit is known with such clay, near Kazatin. As an ornamental stone, they use solid blue and dark red variety – pipe stone, or combarbalite from a deposit in Chile, which contains admixtures of coloring minerals. Similar solid crusts of kaolinite of bluish and greenish hue are known in the Ukraine, on Crimea, at Alushta, under the name alushtite.

Ceramic is burnt clay, from Gk. “keramos” – clay; it is an artificial material on a basis kaolinite. Processing of primitively burnt ceramic produce was known even in the Stone Age. Beads from such ceramic, colored blue after lazurite and green after malachite, were manufactured in Egypt, 7,000 years ago. At the same time, unglazed produce of small form was made – terracotta. When glass was invented, ceramic was covered with glaze. Faience is glazed, non-translucent ceramic, composed on 83% from clay. In 1583-1328 B.C., in Ancient Egypt, such ceramic was widespread for manufacturing of adornments and for imitation of turquoiseturquoise faience, lazuritelapis lazuli faience and others. The European name faience was used after Tuscan Faience, where since the end of the 15th cent., they have produced ware from faience in numerous workshops. In 206-220 A.D., in China, they invented the method of manufacturing of porcelain from white kaolinite clay. Porcelain can be unglazed – biscuit porcelain, or covered with glaze. Such glassy, translucent ceramic is made with annealing under high temperature. There was the time, when they payed for a porcelain cup such volume of gold, which could be put into it; sometimes porcelain was mounted in silver. The flourishing of porcelain manufacture in China fell at 1368-1644. Since the 16th cent., porcelain manufacture has been opened in Korea and Japan, and in Europe it has been known since 1703. Porcelain factories were opened in Germany – in Meissen, in France – in Sèvre, in Austria – in Wien. The first work of art from Meissenian porcelain appeared at the trade-fair in Leipzig in 1710. In Russia, the beginning of porcelain manufacturing fell at the middle of the 18th cent. Examples of adornments from porcelain are cameos from the factory of Wedgwood in England, so called Wedgwood, which were used as insets in jewelries. In France, in Sèvre, they manufactured jewelry porcelain with fused gilding or painted ones. In England, porcelain was decorated with gemstones – emeralds, garnets and others. In royal residences, cabinets with collections of porcelain work of art appeared. In 1914-1924, in Germany, at the Meissen manufacture, they produced small series of porcelain coins from red porcelain or from white one – biscuit porcelain.

Synonyms. Balin, from Balin Dist. in Mongolia | Porcelain earth | Porcelain jasper | Keffekeilite, from Pers. “koeffe” – foam and “gil” – clay | Lithocolla, from Gk. “litcolla” – stone putty | Nakrit, Germ. | Teratolith, from Gk. “tera” – wonder and “litos” – a stone.

Allophane (Allophan—Allophane—Аллофан) (Stromeyer, F. 1816), from Gk. “allos” – another and “phainesthai” – to appear, after its changing of appearance in a blowpipe flame. Composition – Al2O3·SiO2·H2O, an amorphous mineraloid, classified as hydrous aluminum silicate, subclass sheet silicates. Hardness 2.5-3. Density 1.9. Glass luster. Fragile. Allophane is close in its content to kaolinite. It looks like variscite and opal. In mixture with hyalite it forms solid, kidney-shaped and stalactite-like accumulations and glassy masses – hyaloallophane. In its pure form it is white. Transparent to translucent. Ferrous allophane is red-brownish; it contains admixture of goethite. Mixture of opal allophane with variscite is apple-green, light blue or blue; with malachite – green; with chrysocolla – green chrysocolla allophane. In amorphous, glassy opal of turquoise color – aidyrlite there are admixtures of allophane and gibbsite.

In Russia, in the South Urals, allophane was found at the Uchaly Dist. and Bakal’skoye deposit. In Armenia, in turquoise of the Tekhut deposit, the content of allophane admixture reaches 50%. In Georgia, it is found together with turquoise at the Madneuli deposit. In the Ukraine, in the region of Berehove, Zakarpats’ka, allophane exists in the content of porcelain-like or glassy, transformed volcanic rocks of white, gray, yellow and brown color. In Poland, green and blue allophane – Razoumovskyn was extracted at the Sklyary deposit. In Czech Rep., as stalactites of sky-blue color at Zlaté Hory, Czech Silesia. In jewelry bright colored varieties of allophane are used for small produce and insets, usually they contain admixtures of noble opal and chrysocolla. Allophane absorbs paints well, that’s why it is used for imitation of turquoise and other gemstones.

Synonyms. Allophanite | Aidyrlite, after the Aidyrlinskoye deposit, South Urals, Russia | Ehrenbergit | Elhuyarit, after the deposit near Frisdorf, Germany, found in lignite | Ferriallophane | Razoumovskyn (razumovskyn), after the Russ. mineralogist G.K. Razoumovskiy (1750-1831) | Polychromic resin | Riemannit, after the Germ. researcher Riemann.

Dickite (Dickit—Dickite—Диккит) (Ross, C.S. & Kerr, P.F. 1930), after A.C. Dick (1883-1926), a Scottish metallurgical chemist. Composition – Al4[(OH)8|Si4O10], monoclinic analogue of kaolinite. Hardness 1. Density 2.6. Like kaolinite it is represented only in the content of gemstones. In Russia, in the Middle Urals, there is the Shaytanka deposit of perelift. In this gemstone dickite, together with pyrite, form powdering on the surface of growing of quartz aggregates. That’s why earlier perelift was called dickite-quartz. Under the natural oxidation or annealing of perelift, this powdering displays wavy texture of the stone and makes it reddish. Ornamental agalmatolite from Kara Cheku deposit of South Kazakhstan consists mainly of dickite with small admixture quartz, corundum and alunite. In the Ukraine, at the Beregovskoye deposit, ornamental alunite contains also significant admixture of dickite. Among the other ornamental stones with dickite in the content, we should mention bauxite, porcellanite and phyllite.

Ornamental rocks. Such rock as pelicanite contains of mixture of opal and minerals of the group of kaolinite, including dickite. Its solid varieties with the predominance of opal are available for processing and are used as ornamental stones. In the tombs of the 10-11ss cent. in the Volhynia Region, Ukraine, they found beads from pelicanite, called after the Lithuanian researcher V.V. Pelican. Its findings here are available in Kazatin locality. Porcellanite – siliceous schist, usually it contains admixture of clay material, including dickite. In Slovakia, porcellanite is called clay marl; it is known at the Bucnik deposit, near Bystrica. Its texture resembles those of ruin marble of Italy. The name porcellanite, or porcelain jasper is used also for burnt clay rocks of red hue from coal deposits. They are formed under fire at coal mines as a result of dehydration of clays, which transfer into solid rock with conchoidal fracture. Its analogue is artificially annealed kaolinite under the trade name kaolite. Solid varieties of kaolinite under the name terra rossa, or red earth were used in stone-carving and for non-expensive adornments. Phyllite, from Gk. “phyllon” – a leaf, because it’s lamellar structure, a rock with admixture of dickite, formed as a result of metamorphism of shales. Its massive, fine-grained varieties can be of some interest as ornamental stones. An example is ferrous phyllite,as well as quelled Pechenga phyllite from Russia at the Kola Penin. with ornamental inclusions of crystals of pyrite.

Halloysite (Halloysit—Halloysite—Галлуазит) (Berthier, P. 1826), after Baron Omalius d’Halloy (1707-1789), who first noted the mineral. Composition – Al4[(OH)8|Si4O10]·2H2O, polymorph variety of dickite, monoclinic system. Hardness 1-2. Density 2-2.2. In its pure form it is known in the U.S.A. as white porcelain clay – indianaite, called after the discovery location in Indiana State. In New Mexico State, halloysite in mixture with turquoise is olive-green; it is used for imitation: Halloysite with admixture of steatite forms dark green rock – pseudosteatite. In Azerbaijan, near Dashkesan, there is the Zaglik deposit of pseudosteatite. In Austria, it is discovered at the Leoben deposit, Styria. In China, it is extracted together with kaolinite in the Jiangxi Prov. at the Tsvindejang deposit. Inclusions of halloysite produce weak opalescence in crystals of creedite.

Synonyms. Lenzenite, after the surname Germ. mineralogist D.G. Lenz | Stone fat | Mountain soap.

Gibbsite (Gibbsit—Gibbsite—Гиббсит) (Torrey, 1822), after Col. George Gibbs (1776-1833), Amer. mineralogist, who donated a collection of 12,000 specimen to the Yale University, the U.S.A. Hydroxide – γ-Al(OH)3, monoclinic system. Hardness 2.5-3. Density 2.3-2.4. Glass luster, dull one in aggregates. It is found as small table crystals and cryptocrystalline masses, stalactites and spherical concretions. Color: in complete masses without admixtures it is white; admixtures change its color. Gibbsite is formed in weathering crusts or from low-temperature hydrothermal solutions. Usually it is a rock-forming mineral for bauxite and it can be represented with porcelain-like, colloidal gibbsite – alumogel. Together with allophane it exists in the content of aidyrlite – glassy opal of turquoise color. Bauxite, after the discovery location near Beaux in Avignon, France – it is a rock composed with gibbsite and minerals of the group of kaolinite with admixture of diaspore and other hydroxides of aluminum. Polychromatic massive and brecciated varieties of bauxite, jasper-like bauxite and also brecciated bauxite and multicolored bauxite are used as ornamental stones. In Russia, such as jasper-like bauxite from the Krasnaya Shapochka deposit of the Northern-Urals bauxite-containing region and multicolored bauxite – breccia of limestone with bauxite cement from deposits of the Chelyabinsk Region, the South Urals. On the western slope of the Priuralia Territory, at the Zhuravlinskoye deposit and other deposits of gibbsite, together with alunite and halloysite, it forms snow-white, porcelain-like concretions. In the U.S.A., they use bauxite as an ornamental stone; it is a conglomerate of cemented sphaerolites of gibbsite.

Imitations. Gibbsite with admixture of paints and plasticizer, and sometimes with crystals of pyrite is used for imitation of turquoise. Gilson synthetic turquoise consists of gibbsite. Identical in the content with gibbsite – synthetic bayerite, in mixture with copper phosphate, is used for imitation of turquoise – neolithe.

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