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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

PYROXENE, GROUP: AUGITE, HEDENBERGITE , AEGIRINE, ENSTATITE


PYROXENES family (Pyroxen-Familie—Pyroxénes—ѕироксены) (Haüy, R.-J., 1796). Groups name from Gk. “pyr” – fire and “xenos” – a stranger, because it was mistakenly thought not to be a primary mineral of igneous rocks. From this group the most popular minerals, described in separate entries, are diopside, spodumene, jadeite with kosmochlor and omphacite. Lower we describe aegirine, augite, enstatite, hedenbergite, which are sometimes among gemstones according their properties, or they are in the content of ornamental stones. Pyroxenes are similar with minerals of the group of amphibole, they differ from them with angles of cleavage: 124° and 55°, and pyroxenes –– about 90°.

Properties. A group of minerals classified as silicates, subclass chain silicates. Hardness 5-6.5. Density 3.1-3.6. Fragile. Cleavage on prism under the angle of ~ 90°. Pyroxenes are found as prismatic crystals, radial-rayed, twisted-fibrous and grained aggregates, which are classified as orthorhombic or monoclinic system. In a slab perpendicular to the long axis their crystals possess octagonal shape with characteristic appearance of cleavage under the angle close to the right one. Transparent to non-transparent. Color: depending on the content of Iron from almost colorless and pale green to brownish-green and black. An exclusion is a colored variety of diopside – violet-blue violan. For ornamental varieties of pyroxenes massive forms are typical in the shape of grained, sheaf-like, spherolitic, fibrous and twisted-fibrous aggregates.

Augite (Augit—Augite—јвгит) (Werner, A.G. 1792), name from Gk. “auge” – bright, after the appearance of its cleavage planes. Composition – (Ca,Fe)(Mg,Fe)[Si2O6], monoclinic system. A wide-spread specimen of the group of pyroxenes. Color: green, brownish to black. In crystals coloring is zonal or sectorial. Augite is found in the shape of short-columnar brown-red crystals; it is a rock-forming mineral of basalts and diabase – basaltic augite. Transparent and translucent crystals of green augite are used as non-expensive material for faceting. Non-transparent black augite from China is sold in cabochons under the trade name Chinese onyx. In Russia, findings of collection crystals of augite up to 10 cm. long are known in the Urals, in alkali rocks of the Ilmeny Mts. and Nyazemskie Mts.; and also in basalts of the Minusinsk depression. In Kazakhstan, at the Karakamys deposit, the desert of Betpak-Dala, they extract fine-grained black quartz-diabase, or black granite, which is used in stone-carving. In Czech Rep., findings of augite are known near Teplice and Lukov; in Austria – in effusive of Tyrol; in the U.S.A. – on Hawaii. In France, in weathered vulcanite of the Auvergne Dept., they extract well-formed crystals of Auvergne pyroxenes up to 3 cm. long, which are of interest for collectors. In Italy golden-yellow crystals acmite-augite is found on Vesuvius, and in the Piedmont.

Synonyms. Basaltine, obs. | Augite-bronzite | Leucaugite | Octobolit | Prothéite, from Gk. “Protheis” – the Sea-god | Black schorl | Volcanic schorl | Augite spar | Shining stone | Virescite, from Lat. “viridis” – green, after its color.

Hedenbergite (Hedenbergit—Hédenbergite—√еденбергит) (Berzelius, J.J. 1819), after M.A. Ludvig Hedenberg, a Swedish chemist and a coworker of Berzelius, who analyzed and described the mineral. Composition – Ca(Fe,Mg)[Si2O6], monoclinic system. Color: brown-green, dark green to black. As a gemstone it has no importance of its own. In Russia, at the Dal’negorskoye deposit, Primorskiy Region, radial-rayed aggregates of black-green hedenbergite, up to 10 cm. long, are ornamental components of hedenbergite-wollastonite skarns. These skarns are used mainly for manufacturing of big souvenirs: vases up to 25 cm. high, balls, caskets and others. In the Moscow subway, hedenbergite-wollastonite skarn was used for coating of the columns in the station “Petrovskaya-Razumovskaya”. In Uzbekistan, at the Ingichka deposit, the biggest crystals of hedenbergite – asteroit are known, up to 50 cm. long. They are popular as collection samples. In Sweden, in the region of Nordmark, crystals of hedenbergite reached 14 cm. long. In Australia, splendid green to brown-green columnar crystals up to 5 cm. occur at Broken Hill deposit, New South Wales. In India, at a deposit in the region of Skardu, Jammu and Kashmir (disputed area), they extract crystals of black hedenbergite. After processing its cabochons display the effect of cat’s-eyehedenbergite cat’s-eye. In Greece, on the Serifos Is., and in Mexico, at the San Antonio mine, Chihuahua, hedenbergite is found as inclusions in quartz.

Synonyms. Asteroit | Bolophorite (bolopherit) | Funkite, obs. | Lotalite (lotalalite),after the disovery location in Lotal, Karelia, Russia | Skarn, old term of Swedish miners – empty rock | Hedenbergite skarn | Landscape skarn | Primorskiy skarn.

Aegirine (Aegerine— Ægirine—Ёгирин) (Esmark, J. 1835), after “Aegir” – a Scandinavian god of the sea, because it was discovered at first in Norway. Composition – NaFe3+[Si2O6], monoclinic system. Usually it is represented with long-prismatic to fine-needle crystals acmite, which form radial-rayed aggregates and sphaerolites. Color from green to black. In Russia, on the Kola Penin., in the Khibiny alkali massif, there are veined bodies up to 100 m. long with ornamental rocks of figured tinguaite. This fine-grained alkali rock is composed on 50-70% from aegirine, up to 40% from plagioclase and up to 2% from nepheline and other minerals. Especially ornamental are tortoise tinguaite, which possess marvelous “tortoise” texture. In solidity and viscosity tinguaite is not inferior to nephrite and it is well polished, and dark green hue gives a possibility to call it aegirine jade. Another aegirine-containing veined rock of alkali pegmatites from the Kola Penin. is albitite. On its snow-white background very beautiful are rosette-shaped, fine-needle and twisted-fibrous aggregates – aegirine suns. Because of this translucent albitite is called Kola hair stone. In Yakutia, in the Murun alkali massif, aegirine suns up to 3 cm. in diameter are an ornamental component in some varieties of charoite. In the Ukraine, at the Zheltorechenskoye deposit, ornamental ferrous quartzite contains ornamental inclusions of green aegirine. In Greenland, crystals of aegirine up to 10 cm. were found in alkali massifs Ilímaussaq and Narsaarsuk (Narssârssuk). In South Africa, in Malawi, in the Malosa Mt., there were findings of long-prismatic crystals of aegirine in the shape of “pencils” up to 20 cm. long. In Southern Norway, at the Eiker deposit, near Kongsberg, crystals aegirine reached 30 cm. in length. On Madagascar, transparent crystals of gem-quality aegirine, 3x3 cm. in size, were found in the south-eastern part of the country, in miarolitic cavity of orthoclase-microcline pegmatites of the Itrongay deposit, Toliara Prov. In the U.S.A., columnar crystals aegirine up to 20 cm. in length was found on Magnet Cove deposit, Hot Spring Co., Arkansas. In Canada, in the Mont St Hilaire, Québec, they reach 5 cm. long, and at the London mine, Ontario Prov., they extract ornamental syenite with spotty texture. This rock is called leopard stone because of its spotty texture, which depends on ellipsoid isolations of red microcline in black-green mass of aegirine with admixture of hornblende, epidote and other minerals. Such aegirine-containing ornamental rocks are cut in cabochons, flat insets, brooches and also they are used as material for stone-carving.

Enstatite (Enstatit—Enstatite—Ёнстатит) (Kenngott, A. 1855), from Gk. “enstates” – an opponent, is alluding to its refractory nature. In old works it was sometimes called hypersthene. Composition – (Mg,Fe)2[Si2O6], orthorhombic system. It was discovered for the first time in Czech Rep., near Ζdár Mt., in the Erzgebirge. It is represented with flattened and table crystals up to 50 cm. long, as it is in South Norway, in the region of Bamle. Transparent to non-transparent. Color: green, brown-green, more often colorless. In South Africa, in the process of exploiting of kimberlitic pipes, they extracted sometimes emerald-green of chrome-enstatite. In Tanzania, at the deposits Mpwa Mpwa and Mairimba Hill they extracted gem-quality crystals of enstatite. On Sri Lanka, at the Embilipitiya deposit, they found its crystals up to 5 cm. long. In South India, at the Nämakkal deposit, Tamil Nädu, they extract enstatite, which displays asterism with the six-radial star after processing. In the Jammu and Kashmir State (disputed area), near Astor, they discovered a locality of transparent green crystals of a rare monoclinic pyroxene – clinoenstatite. At the placers of Myanmar (Burma), Sri Lanka and the U.S.A., Arizona, they find graveled crystals of gem-quality enstatite of gray-green and brown hue, including those with chatoyant coloring – enstatite black cat’s-eye. Such crystals of enstatite were found in Canada near the Labrador Penin., on the St Paul’s Is., where it is called paulit. Transparent varieties of enstatite are faceted. Non-transparent and translucent rocks with asterism, aventurescence and the effect of cat’s-eye are cut in cabochons, up to 8 ct. In the Smiths. Inst., Wash., the U.S.A., they expose the biggest faceted enstatite from Sri Lanka, 11 ct., and star enstatite 34.8 ct.; and in the Royal Ontario Museum – a faceted green enstatite 12.97 ct. and numerous stones with asterism and the effect of cat’s-eye.

Bronzite is a variety of enstatite, characterized with golden metallic luster on the cleavage planes. After replacement of enstatite or bronzite with light green serpentine in macro crystalline rock – bastite, or schillerstone, it displays silky luster and iridescence, that’s why it is used as an ornamental stone. Some crystals of bronzite also display chatoyancybronzite cat’s-eye, or asterism with the four-radial star bronzite. Similar bronzite was found at deposits in the south of India, near Mysore; in Austria, at the Kraubath deposit, Styria. Serpentinous bronzitite of the Corsica Is., France, is called Corsican verde, Corsican green or schiller quartz.

Hypersthene, from Gk. “hyper” – over and “stenos” – strength, because its hardness is higher than that one of amphiboles, to which it was classified. Now hyperstene usually name ferro-enstatite. It is found as flattened crystals of dark brown to black hue with metallic luster on cleavage planes. Such crystals display aventurescence because of inclusions of native copper and chatoyancy like hypersthene cat’s-eye in cabochons. Such crystals of hypersthene were found at deposits of India; in the U.S.A. – in Oregon, in the Cascade Mts.; in Arizona. Findings of gem-quality hypersthene are known in Finland, Norway, Greenland and Mexico. In Germany, in the region of Bodenmais, they discovered collection crystals of hypersthene 4 cm. long. Another gem-quality variety of hypersthene contains inclusions of plate brookite oriented along cleavage planes. These inclusions on the dark background of hypersthene from a beautiful mosaic of red spots, and sometimes they lead to asterism. Similar material is extracted in the north of Iran, near the Demavend Mt.; it has the trade name ficinit.

Synonyms. Enstatite – Acmite, from Gk. “akme” – acme or sharp, after the typical the form of crystals | Bastite, after the Bast deposit, Harz, Germany; syn. diaclase, or diaclasite | Bronzite, after the typical luster | Chladnite | Green garnet | Paulit, after surname Germ. Geologist H. Paul. | Pegamite | Chatoyant spar.

Ornamental rocks. Among pyroxenes-containing rocks used as ornamental stones we should mention some gabbro, basalts and dolerites. Gabbro is clearcrystalline, macro grained rock of magmatic origin, almost half of which is composed with pyroxenes. An example of its ornamental variety is globular gabbro with spherolitic texture. Sphaerolites of concentric structure are very picturesque in big carved work of art like vases and tables. In Kyrgyzstan, on the northern slope of the Alayskiy Ridge, they discovered pyroxenites with big insets of chromium-containing aegirine-diopside. Insets are mostly not crackled, transparent, dark green, up to 15 mm. wide. They give beautiful color and the effect of translucency to the rock, that’s why this rock is used as an ornamental stone. Another ornamental variety of gabbro, called star gabbro, is discovered in the Chineiskiy massif in East Siberia, Russia. It is a light colored rock, represented mainly with anorthosite with black radial-rayed aggregates of pyroxenes or titanomagnetite up to 2 cm. in cross-section. A variety of this rock in Canada is an ornamental leopard gabbro, or leopard stone from the region of Air Lake, Québec Prov., which is characterized with spotty texture because of light colored isolations up to 12 cm. in size on the dark background of transformed plagioclase. Among ornamental stones are also Thulite gabbro (See zoisite), violet gabbro (See plagioclases), spinel gabbro (See spinel) and smaragdite gabbro. Basalt is a volcanic analogue of gabbro with fine-grained basic mass and rounded cavities of gas bubbles – almond-shaped basalt. Mineral packing of these cavities makes these basalts ornamental. In the content of this packing of the cavities includes agate, carnelian, quartz, calcite, zeolites and others. Those are freckled basalts with analcime in voids, the size of a pea. In Japan, basalt with packing of voids with crystals of xenotime and zircon is very popular – it is called chrysanthemium stone. Dolerite is a medium-grained analogue of basalt. Its massive black variety composed with plagioclase – 40%, augite – 38%, micropegmatite – 20% is called black granite. In the process of serpentinization it is transformed into metadolerite, or greenstone, green-stone rock indistinguishable from serpentinite. This variety of dolerite is used as a coating and ornamental stone.

Synonyms.Eye diorite | Globular diorite | Orbicular gabbro | Variolitic gabbro.

Basalt – Kiku-ishy, Jap. | Kiku-kwa-seki, Jap. | Chrysanthemium stone.

Dolerite, from Gk. “doleros” – delusive, because of its similarity with green schist. In the U.S.A. – syn. diabase.

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