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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

ZEOLITE, GROUP: MORDENITE, NATROLITE, THOMSONITE, STILBITE, ANALCIME, POLLUCITE


ZEOLITES group (Zeolithe—Zéolites—Цеолиты) (Cronstedt, A.F. 1758). A group name from Gk. „zeon” – to boil, is alluding to the characteristic intumescence’s of zeolite minerals in response to heating, that’s why zeolite is also called hydrite. A group of minerals of the class of silicates, the subclass of framework silicate. Here, we perform only those which are of gemological interest. According their structure they can be classified into three subgroups: the first and the second ones are fibrous and lamellar zeolites – they are of monoclinic and orthorhombic systems; the third subgroup of zeolites is of cubic system. Fibrous zeolites are mordenite, natrolite and thomsonite. Lamellar zeolite is stilbite. Analcime and classified together with zeolites pseudocubic pollucite are of cubic system. We are describing them in this consecution.

Mordenite (Mordenit—Mordénite—Морденит) (How, H. 1864), after its discovery location near Morden, Kings County, Nova Scotia, Canada. Silicate – (Na,Ca,K)6[AlSi5O12]8•28H2O, orthorhombic system. Hardness 4-5. Density 2.1. Glass luster. Non-transparent to translucent. Mordenite, as any other zeolites, forms sphaerolites and twisted-fibrous aggregates of white, greenish-gray, reddish to brown color. It is found in the form of veins and amygdales in Rhyolite and andesine and alas well as a product of transformation of volcanic glass. Massive ornamental material is cut in cabochons.

Deposits. In Russia, mordenite was found in significant volumes at deposits of Icelandic spar in Evenkia, Krasnoyarsk Region. Among the largest of them there is one in the basin of the Lower Tunguska River, another one in the region of the settlement of Tura, the Krutoye deposit and another one on the Nidym River. Fine-fibrous aggregates of mordenite form beautiful hair stone in transparent crystals of calcite. In the Ukraine, on the slopes of the ancient volcano Karadag Mt., on the Crimea they find green mordenite rock – trass cemented with chalcedony, which is used as an ornamental stone. In Great Britain, large accumulations of mordenite were observed at the Ballindean deposit in Scotland. In Italy, similar volcanic tuff with less content of chalcedony is known as puzzolan. In Japan, they have cut out a statue of Buddha from this material. There is also the Kawazu deposit, Shidzuoka Pref., with accumulations of mordenite in volcanic tuff. In India, in the region of Poona, there is the Chinchwad deposit of mordenite. In the U.S.A., mordenitic trass of brown, yellow and blue color with landscape pattern is known in Oregon, near Biggs on the Colombia River, where it is called Biggsian jasper. In Canada, at a deposit near Morden, New Scotland (Nova Scotia) Prov., fibrous aggregates of mordenite display the effect of cat’s-eye when polished. In Brazil, gem-quality mordenite is extracted in the Rio Grandi do Sol State. In Mexico mordenitic tuff was used in the construction of pyramids.

Synonyms. Mordenite – Fliokite, after the Sweden Viking Floki Vilgedarson | Ptilolite | Pseudonatrolite | Steeleite, after the Engl. collector of minerals J. Steel.

Ornamental rocks.Landscape stone | Trass, from Ital. “terasso” – planking, after the form of depositing | Chalcedonic trass.

Natrolite (Natrolith—Natrolite—Натролит) (Klaproth, M.H. 1803). The name reflects its sodium (Lat. “sodium”) content. Silicate – Na2[Al2Si3O10]·2H2O, orthorhombic system. Hardness 5-5.5. Density 2.2. Glass luster. Fragile. Cleavage in one direction. Color: white, rose, red and brown-yellow, it can be dark green because of admixtures, often it is colorless. Transparent to half-transparent. In aggregates non-transparent to translucent. Parallel-fibrous aggregates display silk luster and the effect of cat’s-eye in cabochons. It is found in the form of columnar and needle crystals forming sphaerolites and solid grained masses. It is found in cavities in basalts and as a secondary mineral in alkali rocks.

Deposits. In Russia, on the Kola Penin., gem-quality natrolite in crystals up to 30x15x15 cm. in size in alkali pegmatites of the Khibiny massif is known. In giant crystals of natrolite from the Putelichorr Mt. transparent segments reach the size of 5x6x6 cm. At the Koashva mine, they found natrolite hair stone in the form of transparent crystals with inclusions of needle aegirine. In the Lovozerskiy massif, at the Karnasurt mine, near Lovozero, the most interesting as an ornamental stone is natrolite-albite rock, 40% of its volume is composed with natrolite. The size of separate pieces of white natrolite in this pegmatite body reaches the length up to 1 m. In the central part of the vein, they find chalcedonic-like natrolite in the form of irregularshaped veins up to 20 cm. thick. The color of this half-transparent ornamental variety can be gray, brownish, wine-yellow, pale pink to lilac. The dispersion of color in veins is even, stripped and spotty. In nepheline syenite, when nepheline is replaced with natrolite, multicolored reddish rock is formed – spreustein. Some spreusteinized urtites or lujavrites can be used as ornamental stones. At some parts of apatite deposits they form the zones up to 20-30 m. thick. In Denmark, on the Faeroes Iss., they discovered natrolite with the effect of cat’s-eye in cabochons. In Great Britain, colorless natrolite – galactite is known in the form of solid columnar aggregates at the Bishopton deposit, South Scotland; and in Northern Ireland – at the Enthrim deposit, near Belfast. In Norway, crystals natrolite up to 20 cm. and exceptionally to 50 cm. occur in larvikite and their pegmatites in Langesund Fjord; also red natrolite with the local name fargite, near Glenn Farg; and dark green ferrous natrolite, near Brevik, Telemark, are found. In Germany, yellow massive natrolite, available for cut in cabochons, is known. It was extracted in the regions of Roßberg and Darmstadt, Hessen; as well as near Eisenach, Thüringen; and at the Hohentwiel deposit, Baden-Würtemberg. In Czech Rep., natrolite is found as filling of geodes in basalts, near Mariánská Hora, by Ústi nad Labem. In Pakistan, gem-quality crystals natrolite up to 12 cm. in serpentinite Khuzdär Dist., Baluchistan, were found. In Myanmar, there is an ornamental variety of jade-albite – maw-sit-sit jade, in which the white mineral taken for albite is mainly natrolite. In Canada, they made faceted gems up to 15 ct. from crystals of natrolite at the Ice River deposit, British Columbia Prov. In the Québec Prov., crystals of natrolite in alkali rocks up to 15x2 cm. at the Mont St Hilaire. Very large natrolite crystals up to 1.2x1 cm. occur at Thetford mine, Megantic Co., Québec. In the U.S.A., rough material available for faceting is found at the Bergen Hill deposit, near Levingston, Montana. In California, transparent crystals of natrolite as additional material at the Benitoite Gem mine, San Benito Co., were extracted.

Transparent crystals of natrolite are faceted sometimes; faceted gems reach 20 ct.

Synonyms. Aedelite, after the Aedel deposit, Sweden | Echellite, from Fr. “échelle” – ladder | Pseudojade | Galactite, from Gk. “gala” – milk | Laubanit | Portite | Radiolite, from Lat. “radius” – Rai and Gk. “lithos” – a stone | Savite, from locality of Tuscany, Italy | Spreustein, from Germ. “spreu” – straw and “stein” – a stone, because of twisted-fibrous natrolite | Acicular stone | Sodic chaff stone | Fibrous zeolite.

Thomsonite (Thomsonit—Thomsonite—Томсонит) (Brooke, H.J. 1820), after Thomas Thompson (1773-1852), Regius Professor of chemistry, University of Glasgow, Scotland (1818-1852), who first analyzed the mineral. Silicate – NaCa2[Al5Si5O20]•6H2O, orthorhombic system. Hardness 5-5.5. Density 2.3-2.4. Glass luster. Cleavage in two directions. Fragile. Transparent to translucent. Thomsonite forms a row of constant miscibility with natrolite. It is found mainly in the form of radial fibrous aggregates and grained masses of white, yellow, red-brown and green tones. Red thomsonite is called triphanite. Besides, there are light blue, orange and black varieties, which display color zones because of mineral admixtures. White-rose thomsonite with typical disposition of concentric colored rings resembling an eyeball is called thomsonite ox-eye. Aggregates of non-transparent and translucent thomsonite display chatoyant luster and the effect of cat’s-eye in cabochons.

Deposits. Thomsonite as amygdales in basic effusive rocks or in alkali rocks is found. In Russia, gem-quality thomsonite is found in basalts of East Siberia, in the Tomsk Region, on the Tom’ River, where its transparent sphaerolites up to 4 cm. in diameter were found. In Transbaikalia, rocks enriched with amygdales of thomsonite in the region of Malyy Kunaley, on the Khilok River, are found. In Great Britain, a superb rose crystal variety of thomsonite – gibsonite is popular; it is extracted in Scotland, on Old Kilpatrick Hills and at Barrhead, near Glasgow. In Northern Ireland, a massive mahogany variety thomsonite – chalilite in Antrim Co was found. In the south of Norway, significant findings of thomsonite are known in the Langesund region. On the Faeroes Iss., Denmark, radial fibrous ball-like aggregates of thomsonite are called faröelite. In the north of Czech Rep., ornamental thomsonite was discovered at the Pihel deposit, near Çeská Lípa. In South Africa, it was found in kimberlites of the Jagersfontein deposit. In the U.S.A. on the Ozark Mt., Arkansas, gem-quality massive thomsonite of white or rose-red color is known under the trade name ozarkite. In Minnesota, at the Grand Marias deposit, fine-grained fibrous, olive-green gem quality variety called lintonite. In Colorado, in basalts on Table Mt., near Golden, Jefferson Co., they found zonal colored comptonite in the form of filling of amigdules. This is an agate-like non-transparent rose-green ornamental variety of thomsonite. In New Jersey, thomsonite at the Patterson deposit, Passaic Co., in cavity up to 20 cm. was extracted.

Massive colored varieties of thomsonite are cut in cabochons.

Synonyms. Bagotite, after the discovery location near Bagotville, Ontario Prov., Canada | Comptonite, after the Engl. geologist Compton | Karphostilbite, from Gk. “karphos” – straw and the name of the mineral stilbite, because of the needle shape of its crystals | Koodilite, with admixtures | Lintonite, after the Amer. chemist Laura Linthon, who described the mineral | Mesolitine | Eye stone | Thonsonite | Triploclas | Uigite, after the discovery location in the region of Uig, on the Skiy Is., Scotland | Winchellite, after the Amer. mineralogist N.H. Winchell.

Stilbite (Stilbit—Stilbite—Стильбит) (Haüy, R.-J. 1796), from Gk. “stilbein” – to lustre or shine, or “stilbe”, a mirror, is alluding to its pearly or vitreous luster. It is also called common zeolite or desmine, from Gk “desme” – sheaf-like. Silicate – (Ca,Na)9[(Si,Al)36O72]•28H2O, monoclinic system. Hardness 3.5-4. Density 2.2. Glass luster. Cleavage in one direction. It is transparent in crystals and translucent in aggregates. Color: white, yellowish to brown, red to orange-red. It displays nacre luster on the cleavage planes and silky one in aggregates. Stilbite is found in the form of lamellar, usually splintered crystals, which form massive sphaerolites and parallel-columnar aggregates.

Deposits. It is widespread as filling of cavities and as veins in rocks of different composition, and alas well as a product of transformation of plagioclases and volcanic glass. In Russia, in the Krasnoyarsk Region, Evenkia, gem-quality stilbite in golden yellow crystals up to 10 cm with Icelandic spar at the Amudikha and Nidym Rivers, in the basin of the Low Tunguska River, were found. There, the size of sphaerolitic aggregates of rose stilbite reached 25 cm. in cross-section. On the Faeroes Iss., Denmark; and also in Iceland at the Beruifjord, snow-white crystals stilbite up to 5 cm. in size are found on a deposits Teigarhorn and Helgrustadir. In Poland, in Lower Silesia, stilbite was extracted at the Pilgrammshein deposit, near Strzegom (form. Strigau). In Hungary in pale yellow radial-fibrous aggregates up to 10 cm. at the Dunabogdány deposit, near Budapest, were found. In Italy on the Elba Is., in pegmatites they found large crystals of stilbite. In Australia, in New South Wales, crystals of stilbite are found at the Garravilla area, near Kunabarabran. In India, in the Mahäräshtra State, crystals of stilbite up to 20 cm. at the Pandulena Hill deposit, near Poona, were found; also at the Jälgaon and Nashik in the of Aurangabad region, Mahäräshtra. In the U.S.A., sheaf-like aggregates stilbite up to 10 cm. found at the Paterson, Passaic Co., New Jersey, where his massive brown aggregates displayed aventurescence in cabochons; also stilbite was discovered on the Kuiu Is., Alaska. In Brazil, large crystals of stilbite were found at the Rio das Antas deposit, Rio Grandi do Sol State.

Bright colored differences of stilbite are cut in cabochons. They also use its cross-like twin crystals for adornments.

Analcime (Analcim—Analcime—Анальцим) (Haüy, R.-J. 1797), from Gk. “análkis” – weak alluding to the weak electrostatic charges that develop when it is annealed or rubbed. Silicate – Na[AlSi2O6]·H2O, cubic system. Forms a series with pollucite. Hardness 5. Density 2.3. Fragile. Glass luster. Transparent to non-transparent. Color: colorless, white, yellowish, greenish or rose. It is found in the form of radial-rayed and massive grained aggregates as well as isometric crystals, which are called cubic zeolite, or cubicite because of their shape. Its transparent and half-transparent crystals enriched with inclusions of native copper are of interest for processing. They display aventurescence in cabochons.

Deposits. Analcime is a typical mineral of contact-metasomatic deposits in basalts. In Russia, on the Kola Penin., in the Khibiny and Lovozero massifs, the biggest colorless crystals of analcime to 30cm. were found. In the Krasnoyarsk Region it was to 20 cm. long and to 3 kg. weight at the deposits of Icelandic spar: Krutoye, Ozernoye, in the basin of the Lower Tunguska River and on the Nidym River. In Khakassia, Krasnoyarsk Region, brick-red massive volcanic tuffs of “caviar” structure containing analcime can be classifies as an ornamental stone. After the main mineral component this rock is called analcimite. In Georgia, crystals of analcime up to 15 cm. are found at the Shorapani deposit, K’ut’aisi Region. In Italy, crystals of analcime up to 14 cm. were extracted at the Frombach deposit, and in Alpe Ciamol, Val di Fassa, on analcime pseudomorph quartz met, as well as on the Cyclopean Iss. not far from Sicily, where it had been discovered first of all. In India, analcime is found in basalts of the plateau Deccan. In the Indian Ocean, on the Kerguelen Is., France, they find large transparent colorless crystals of analcime. In Canada, gem-quality crystals of analcime up to 25 cm. are known at the Mont St Hilaire, Québec Prov., from which they received a faceted stone in 3 ct. In the south west of Greenland, in the region of Tunugdliarfik Fjord, and in the alkali massif Ilímaussaq they found large crystals of analcime. In the U.S.A., such crystals, available for processing, were extracted at deposits of states of Washington, California and Oregon. In New Jersey and Michigan, they find beautiful ornamental stone aventurine analcime. Because of the small size of its crystals, however, the weight of its cabochons was not more than 0.25 ct. Transparent crystals of analcime are faceted for collection purposes only.

Pollucite (Pollucit—Pollux—Поллуцит) (Breithaupt, A. 1846), after Pollux – the twin brother of Castor in classical mythology, in allusion to its intimate association with the mineral castorit, now renamed as petalite. According the shape of its crystals it is also called cuboite and cubicite. Silicate – (Cs0.7H2O0.3)Na0.3[AlSi2O6], cubic system. Hardness 6.5. Density 2.9. Glass luster. Color: rose, light brown, more rarely light blue and violet. Colorless crystals are often with white inclusions. It forms pseudomorphs on petalite and spodumene. It forms an isomorphic row with analcime. It is found mainly in the form of isometric crystals with transparent segments and as massive fine-grained aggregates.

Deposits. Pollucite is found in cavities of granite pegmatites. In Russia, it was found in pegmatites of the Kola Penin., in the Vasin Myl’k Mt., Voron’i Tundry. In Rep. of Tyva, pollucite was extracted from pegmatites in the Sangilen Ridge, as well as in Central Transbaikalia, in oligoclase pegmatites of the Malkhan Ridge. In Tadzhikistan, in the South-West Pamirs Mts., pollucite in crystals up to 5x3 cm. in size was discovered on the Vez Dara deposit, in the region of Khorugh. In Europe, its findings are known in Finland, at the Viitaniemi deposit, near Tampere, and in rough crystals up to 50 cm. in pegmatite at Luolamäki, In the north of Sweden, massive violet-pink pollucite was extracted at the Varuträsk deposit to the west from Shellefteo. In Great Britain, it was found at the Meldon deposit in Devon. In Italy, on the Elba Is., crystals of pollucite up to 12 cm. in cross-section were found at the Speranza deposit, where it was discovered for the first time. In Africa, pollucite was found in Namibia – at the Karibib deposit; in Zimbabwe – at the Bikita deposit; in Mozambique – in the Alto Ligonha region. On Madagascar, at the Manjaka deposit, near Ikhosy, pollucite was found together with rubellite in rare-metal pegmatite. In India, in the Jammu and Kashmir State (disputed area), its crystals up to 15 cm. were extracted from pegmatites near Nagar and Shengus, in the region of Gilgit. In Afghanistan, transparent colorless crystals of pollucite up to 20 cm. in cross-section were found at the deposits Kulam and Paprok, Nuristan; and in the Kunar Prov., in pegmatites they reached 60 cm. in cross-section. In the U.S.A., in Maine State, massive gemmy pollucite and its transparent rose, straw-yellow and colorless crystals were extracted from pegmatites of Bennett quarry, Oxford Co. They made faceted gems up to 9 ct. for collection purposes from them. In Canada, pollucite was discovered at the Tanco deposit pegmatite in the Manitoba Prov.

Bright colored massive varieties of pollucite are cut in cabochons. Transparent crystals are faceted for collection purposes. In the Smiths. Inst., Wash., there are faceted colorless stones in 7 and 8.5 ct.

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