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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

PYROPHYLLITE, GROUP: PYROPHYLLITE, TALC


PYROPHYLLITE group (Pyrophyllit—Pyrophyllite—ѕирофиллит) (Hermann, R.H. 1829), from Gk. “pyr” – fire and “phyllon” – leaf, is alluding to its exfoliation when strongly annealed. Here also talc is described, sheet silicate of monoclinic system, close to pyrophyllite in structure and properties.

Composition & Properties. Silicate – Al2[(OH)2|Si4O10], subclass sheet silicate, monoclinic system. Hardness 1-2. Density 2.6-2.9. Cleavage in one direction. Glass luster, pearl one in fine-plated aggregates, dull one in massive aggregates. Greasy by touch. It is not decomposed in acids. Pyrophyllite is found as plate crystals up to 3 cm. wide, which form radial-rayed aggregates and sphaerolites. Color: brownish, bluish, white, pale yellow, apple-green, reddish with admixtures of iron. It is translucent in fine plates. Pyrophyllite as itself is of no gem-quality significance, where cryptocrystalline masses of fine-flaked agalmatolite are used. Properly it is a rock, composed mainly with pyrophyllite, not rarely with significant content of kaolinite, dickite, sericite, sometimes talc and other admixtures. Ornamental varieties of agalmatolite are dark green verdolith, or neurolite with admixture of quartz and pinite enriched with muscovite. Presence of admixture of hematite makes agalmatolite cherry-red in color, and admixture of cinnabar – blood-red. Argillite is a cryptocrystalline rock close to agalmatolite in the composition; it is composed with clay minerals with admixture of pyrophyllite, small parts mica and quartz. Its color is from white to brownish of different tones, which depend on the content. Not rarely it is used in stone-carving.

Deposits. Agalmatolite is formed on aluminiferous rocks in the process of their metasomatism, more rarely in the process of metamorphism of the rocks. It is well-known. It has been extracted in many countries since long ago. In Russia, pyrophyllite was discovered at first in the Middle Urals by the Russian chemist R.F. Germann. It was discovered in quartz veins of the Staro-Pyshmenskoye deposit (now the Berezovskiy mine), near Yekaterinburg. In Pribaikalia and Transbaikalia, there are numerous deposits of agalmatolite. Along the Talaya River, near Slyudyanka, they find grayish-green agalmatolite, and along the Nizhniy Biboy River, a tributary of the Onot River, it is violet-gray. In Buryatia Rep., there is the Byrkhe Shibirskoye deposit of agalmatolite in the Khorinskiy Dist., with polychromatic rough material. In the Rep. of Tyva, there are the Bai Taginskoye, Kyzyl Dag and Sarykh Khainskoye deposits. In the Primorskiy Region, they found the Bikinskoye deposit; and in the Magadan Region – Nevskoye. In the Ukraine, there is one of the most ancient deposits of agalmatolite of metamorphic origin – Zbranky in the area of Ovruch. In Azerbaijan, there is the Sharukarskoye deposit. In Kazakhstan, they exploit the Maitobinskoye deposit near the railway station of Maitobe, and the Kara Cheku deposit in the Alma-Ata Region. In Uzbekistan, near the railway station of Barrazh, on the southern slope of the Karjantau Ridge, there is the Ak Tash deposit; and in the Tashkent Region, on the northern slope of the Kuraminskiy Ridge there is the Kal’makyrskoye deposit. In Romania, agalmatolite was known at the Bâita Bihor deposit in the shape of translucent brownish and greenish aggregates under the local name biharit. There is serpentine, talc and calcite in its content. In East Asia, deposits of agalmatolite are in Mongolia – Erdenet and Ikh Shankhai; in Cambodia – Trasey; in Vietnam – Tanmay; in the south of Laos – Khouienamkong; in Japan – in Nagano Pref. and others. In China, many deposits of agalmatolite have been known since the deep antiquity and they have been exploiting till nowadays, for example, Shoushan, Fujian Prov. In South Africa, ornamental dark green pyrophyllite rock with significant admixture of epidote and rutile, from the valley of Ottosdal, North-West Prov., has the trade name verdolith, koranna stone or South African fairy stone. In Australia, ornamental white argillite is popular under the local name zebra, because of the pattern with red stripes and spots. It is extracted at a deposit near Kununurra, East Kimberley. In the U.S.A., in California, North Carolina, Wisconsin and other, a traditional material for Indian carved produce is agalmatolite, known under the trade name catlinite. Its content is pyrophyllite, kaolinite with admixture of muscovite, diaspore and hematite. In Canada, Indians used argillite from the Graham Is., Queen Charlotte Archipelago, British Columbia Prov. for stone-carving. In Brazil, at the Ibitiara deposit, Bahia, plate crystals of pyrophyllite reach 12 cm. long. In Mexico, it gemmy red crystals up to 1 cm at Villa Madero locality, near Madera, was found.

Synonyms. Agalmatolite, from Gk. “agalma” – sculpture and “litos” – a stone, after its usage | Chinese agalmatolite | Agalmatolithus, obs. | Argillite, from Gk. “argilos” – clay | Bildstein, Germ. | Fat | Flint clay | Gemmaguya, obs. | Soapstone | Chinese soapstone | ~ stone: fairy ~, figure ~, ice ~, image ~, pagoda ~, pencil ~, picture ~, sculptural ~, wax ~. | Kolybtash, Uzbek | Koreite | Mudstone | Pagodite, after its usage in sacred sculptures | Restormelite, after the Restormel deposit, on the Cornwall Penin., Great Britain | Roseki, Japan | Wonderstone.

Quality improvement. Agalmatolite can be colored artificially. Its varieties with talc receive beautiful green hue after annealing. When polished, products from agalmatolite are rubbed with wax for additional luster.

Treatment. Agalmatolite is a non-expensive ornamental stone, which has been used since the pre-historic times because of the easiness in processing. Beads and amulets from it were found in ancient tombs. In Kievan Russia, small stone-carving produce from agalmatolite has been known since the 4th cent. They were in fashion in the Ukraine till the early of the 20th cent. In Russia, the Peterhof lapidary factory, SPb., widely used this stone for ash-trays, vases, paper-weights and stamps. In South-East Asia, agalmatolite is often used for imitation of nephrite in sculptures of Buddha and other Chinese gods. In the Museum Hist. Nat., Paris, they expose a large collection of carved works of art by Chinese masters of the 17-19th cent. from red and yellow pagodite. Nowadays, the significance of agalmatolite as an ornamental stone is decreased. Only rarely, it is cut in cabochons, but it is still a traditional material for stone-carvers in Tyva, Buryatia Rep. and also in Japan and Korea. In 1990, at the World Paris exhibition, Kazakhstan represented a wonderful vase from white agalmatolite.

Legends. Astrologers suppose agalmatolite to be a talisman of cookers and confectioners. It helps them to become magicians in their profession.

Similarity. Agalmatolite is close in properties to talc, and sometimes they are mixed up with each other. It differs through coloring in blue with the solution of nitrate of cobalt, after annealing.

Talc (Talk—Talc—“альк) (Agricola, G. 1546), from Arabic “talq” – pure (white), probably is alluding to the color of its powder. Silicate – Mg3[(OH)2|Si4O10], subclass lamellar silicate, monoclinic system. Hardness 1. Density 2.2-2.8. Greasy luster, pearl one along cleavage planes. Perfect cleavage in one direction. Greasy by touch. It is found as massive aggregates, usually fine exfoliated and flaky, rarely in thin tabular crystals. Non-transparent to translucent. Color: silver-white, gray, pale green, dark green, yellow, brownish, reddish – depending on admixtures. There are known varieties with high content of chromium – chrome-talc, and also nickel willemseite. Because of the typical luster, it is called zhirovik, speckstone or soapstone. Solid varieties, more hard because of mineral admixtures, are called steatite, talc-chlorite, agolite and others. They are of special interest for stone-carving. Presence of dendrites of manganese increases the ornamental properties of massive monochromatic steatite. Talc with admixture of serpentinite is called deweylite.

Deposits. It is formed mainly as a result of hydrothermal transformation of ultra-basic rocks or in the process of contact metamorphism of carbonate layers. In Russia, the main regions with deposits of talc are the Middle and South Urals. In the Perm’ Region, there is the Sarany deposit with black and violet talc; in the Yekaterinburg Region: Shabry – with light bluish-green one, Mramorskoye and Sysertskoye; near Nizhniy Tagil – Saldinskoye in the valley of the Salda River. In the Chelyabinsk Region – Medvedevskoye and others. In Bashkortostan – the Kosma-Demyanovskoye deposit and the Kiryabinskiy mine. In the Krasnoyarsk Region, in the Yeniseiskiy Ridge there is the Kirgiteiskoye deposit with the rose talc. In the Kemerovo Region – the deposits Alguiskoye and Svetlyi Klyuch; In the Irkutsk Region – Onotskoye, in the East Sayan Mts., with greenish-yellow talc; in the Khabarovsk Region – Birakanskoye. Among the other countries we should mention Georgia – the South Ossetian Chorchan group of deposits of talc. In Kazakhstan – the Dzhetygara deposit and Kenterlausskiy massif. In Uzbekistan – the Zinel-Bulak and Kazgan-Tauss deposits. In Polish Silesia ornamental steatite is extracted at the deposits Sombkovice and Szklary (form. Kosemitz). In Austria, there is the talc Rabenwaldkogel deposit, Styria; in Germany – Smretschany in Bavaria, and Zöblitz in Saxony; in France – Briançon, Delphinate Dept. In Africa the most ancient deposits of talc are known in Egypt; in Mozambique there is the Limbué deposit, near Lake Malawi (Lake Nyassa); in South Africa – in the area of Barberton, Transvaal. In India, such is Kundoll deposit in the region of Mumbai (form. Bombei). In China similar deposits are on the Liaodong Penin.; there are such deposits in Korea, too. In the U.S.A., deposits steatite is submitted as lenses in serpentinites: at Amity, Orange Co., and at Gouverneur, St Lawrence Co. – in New York; in fine green foliated aggregates at Holly Springs, Cherokee Co., Oregon, and others. Its largest deposits are known in Brazil, in Minas Gerais State, near Oro Prêto, and in Bahia State – at the Brumado.

Talc schist is a rock contaminated with talc known under the trade name talc-chlorite. As an ornamental material in Russia it was extracted in the Urals, at the Berezovskiy mine, and in Karelia, at the Segozërskoye deposit. Because of admixture of quartz and high content of chlorite its hardness is almost thrice as much as those of talc, which provides solidity of produce in spite of some difficulties in processing. According its usage, it was called potstone; and in Germany – topfstein; in Italy – lavezstein (laverstein, lovezstein), from Ital. “lavecco” – a pot; in the U.S.A., in North Carolina, it is called parophite. A silicified variety of potstone has the trade name pottalite, those with admixture of magnetite – ctauberite.

Kerolite is an intermediate variety between talc and serpentine, it is also possesses ornamental properties. Its color is white with yellowish, more rare with light bluish tone. It is cryptocrystalline mineral aggregate, harder than talc and better in polishing. It is found in cavities of serpentinites in weathering crusts. In Russia, in the South Urals, kerolite is known at the Akkermanovskoye nickel deposit. In North Kazakhstan, it was found at the Chugaevskoye deposit; in Uzbekistan – at the Sultan Uiz-Dag Ridge. Kerolite is used only in stone-carving.

Synonyms. Talc – Agalite | Agnesite, from the Agnes deposit, Great Britain | Asbestin | Briançon chalk | French chalk | Spanish chalk | Colubrine, obs. | ~ jade: Fudsjan ~, Hunan ~, Manchurian ~, Shanghai ~, Soochow | ~ stone: fat ~, Chinese figured ~, stream gravel ~, grease ~, mountain ~, sculptural ~, soft ~, wax. | Kerolite, from Gk. “keros” – wax, after the outer shape | Lardite (larderite), from Lat. “lard” | Mussolinite, from Sardinia, after the dictator of Italy Mussolini | Pimelite | Steatite, from Gk. “steatos” – grease. | Chinese steatite | Talcosite | Taufstein.

Talc-chlorite – Balpum, local name in India | Disintribite | Dolerine, talc-chlorite-feldspars schist from the region of Mont Blanc, Rhône-Alpes, France | Giltstein, Germ. | Lardalo, Ital. | Ollite, from Lat. “olla” – miner | Paramoudra, Irish | Pottalite, after J. Pott, Engl. | Steashist | Feldspar steashist, after the content | Oven stone | Talcite, after the content.

Treatment. Talc as an ornamental stone is of interest only for small carved produce and small sculptures because of its low hardness. Sometimes it is improved with coloring. Such is Korea jade, which is used for imitation of nephrite and jadeite. In the 6th millennium B.C., in Ancient Egypt, they made carved necklaces from it, covered with green glaze like malachite, and cut amulets in the shape of scarabs. In the 1st millennium B.C., in Sumer they manufactured cylindrical stamps from annealed steatite. In the 7th cent. B.C., talc was taken from the Cyclades Iss. to continental Greece, where it was used in glyptic. In Brazil, near Oro Prêto, they have been carving cups and small figures from talc since the 17th cent. It was of no less popularity in the East. We can see it in the collections of many famous museums throughout the world. In the Armory Museum Kreml., Moscow, there is a carved icon of the 11th cent., made on talc, with a silver frame, 31.4x26.4 cm. in size; it is an icon image of Dmitry of Solun (Thessaloniki). Nowadays, in West Africa the people of Kissi uses steatite in stone-carving.

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