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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

ZOISITE, GROUP: ZOISITE (CLINOZOISITE, TANZANITE, THULITE)


ZOISITE group (Zoisit—Zoisite—÷оизит) (Jameson, R. 1804), after Sigmund Zois, Baron von Edelstein (1747-1819), Austrian researcher, who financed mineral-collecting expeditions. Its initial name was saualpite, after the discovery location in the Sau Alps Ridge, Carinthia, Austria. Here also clinozoisite is described, which is monoclinic analogue zoisite.

Composition & Properties. Silicate – Ca2Al3[O|OH|SiO4|Si2O7], subclass of diorthosilicates, the group of epidote, orthorhombic system. Hardness 6-7. Density 3.1-3.6. Glass luster, pearl one. Cleavage in one direction. Fragile. Zoisite is found as columnar crystals, their radial-rayed aggregates and solid grained masses. Transparent to nontransparent. Common zoisite is colorless, grayish-white, green and brown. It is rarely found in transparent crystals. Zoisite became well known as a gemstone after the finding of its greenish-blue variety – tanzanite. For jewelry purposes they use also red zoisite – rosaline, pink – thulite, apple green – chrome-zoisite and purple-green – hueblinite. Its green color depends on admixture of iron (Fe3+) and chromium (Cr3+), pink and red one – on manganese (Mn3+) – rosaline, blue – on vanadium (V3+). In artificial light tanzanite displays violet hue. It displays obvious pleochroism from blue to red-violet to green or brown. Plenty of needle inclusions of actinolite-tremolite produce the effect of cat’s-eye in cabochons. Identical in composition with zoisite, monoclinic clinozoisite, or aluminum epidote, differs from it with lighter tones of color (See epidote). Zoisite forms pseudomorphs on vesuvianite and also can be replaced with prehnite. It is a rock-forming material for such ornamental stones as anyolite, zoisitite or zoisite jade, Thulite gabbro and saussurite jade.

Deposits. Zoisite is formed in hydrothermal veins and in alpine veins, as well as in rocks in the process of low-temperature metamorphism under high pressure. In Russia, in the Middle Urals, at the Slyudorudnik mine, they found crystals of zoisite in quartz vein. At the Sarany deposit, Perm’ Region, in transformed gabbro zoisite veins with crystals of olive-green to emerald-green zoisite, up to 5 cm. long, were found. At the Izumrudnye Kopi mines, they found thulite in radial-plated aggregates of pink-cream color. In the South Urals thulite was discovered at the Borzovka mine, Chelyabinsk Region. In the Polar Urals, in skarnoids of the Volodya Key Mt., zoisite forms columnar crystals up to 5 cm. long. Zoisite was also found in rock crystal-containing veins on Novaya Zemlya. In the south of the Kemerovo Region, in Gornaya Shoriya, thulite is described at the Sheregesh deposit. In North-Eastern Transbaikalia, in marbled limestone of the Kodarskiy Ridge, near contact zone with granitoids, they discovered massive accumulations of monomineral thulite of tender pink spotty color easy for polishing and obvious luster.

In Norway, crystals of zoisite at the Arendal deposit were found; and in the regions of Trondheim, Sør-Trøndelag; and Lexviken, Jämtland, they discovered deposits of thulite. It is authorized official gemstone Norway. In Bulgaria, in the massif of Reela ornametal thulite in skarns was found. It also meets in Italy at the Traversella deposit. In Austria, zoisite’s original locality is Sau Alpe or Svinska planina, Carinthia. In Switzerland, also in alpine veins, they found green chrome-zoisite in the Zermatt deposit, Valais canton. In Germany zoisite in Bavaria, in the Fichtelgebirge region was discovered. In 1966, in Tanzania, the tanzanite – “Blue Treasure of Africa” at Karo deposit, near Merlani Hills, in the Arusha area, was discovered. In 2000 in the Mwanza region, they found one more deposit of tanzanite near the Usanga village. Transparent zoisite was represented there with green, light brown and colorless crystals, as well as with bluish-green tanzanite with the content of V2O3 up to 1% and admixture of chromium (Cr3+), with blue vanadium-containing tanjeloffite and purple-green hueblinite. Hueblinite in gem-quality fragments up to 60 gm. was found; faceted stones made from them had the weight up to 2 ct. Transparent crystals of tanzanite can be up to 5x3 cm. in size, more rarely – to 10 cm. After faceting pure stones have the weight up to 2 ct. After annealing faceted stones receive perfect blue tone similar to sapphire. Initially, tanzanite was sold as dumortierite, then as cordierite. Later, a deposit of tanzanite in Kenya was discovered, near the Tanzanian border. It is situated 150 km. from the Merlani Hills deposit and is similar to it. In India (Pakistan), zoisite in colorless or green gem-quality crystals up to 6 cm. at the Alchori deposit and Turmiq Valley, Shigar Valley, near Skardu, Jammu and Kashmir (disputed area).

Ornamental rocks. In the Middle Urals, at the deposits Pervoural’skoye and Sarany, thulite is a rock-forming mineral for thulite gabbro. The similar ornamental stone was extracted in the Polar Urals, in the massif of gabbroids along the Bol’shaya Kharamatolou River, to the south from the railway station of Polyarnyi. Opened massifs of pink gabbro are seen along the river for 500 m. In Norway, abundant blocks of pink finegrained thulite at Sauland, Telemark, were extracted; and at Lom, Oppland; also near Questebek, where thulite-containing rock – thulitite is known. In Italy, thulitite at Traversella, Torino Prov., Piedmont, was found. In 1954, in Tanzania, at the Longido mine was found emerald-green color ornamental rock – aniolite, which contained green zoisite, amphibole and inclusions of non-transparent ruby. In the U.S.A., deposits of thulite are known in several states: California, North Carolina Massachusetts, and Wyoming. In South Dakota, they extracted monomineral greenish-gray zoisitite, which displayed the properties of ornamental stone and was available for method of tumbling. In Pennsylvania, a rock with thulite is used as a jewelry-ornamental stone under the tradename unionite.In Nevada, massive rose-green metamorphic rock, composed with thulite, pink clinozoisite, diopside, scapolite and epidote was extracted in the Lapis Nevada quarry, Pine Mts., Douglas Co. It is used as an ornamental stone under the trade name Nevada lapis. In the process of replacement of feldspar rocks of basic content it is formed fine-grained mineral aggregate of saussurite, composed with zoisite in mixture with other minerals. Because of its grayish-green color this massive rock has received the tradename saussurite jade. It is often used in stone carving, especially for the imitation of more expensive nephrite. Ornamental zoisite in small quantities is found in Canada, U.S.A., Mexico, Scotland, Finland, Namibia and Japan, as well as in Western Australia – near Robern.

Synonyms. Calcium epidote | Chrome-zoisite, after its content | Hueblinite, after the surname of Switzerland gemologist E. Huebeline | Illuderite, obs. | Nephrite prismatic spar.

Tanzanite after the discovery location in Tanzania, the name was offered by G. Platt, the vice-president of the firm of Tiffany & Company in the U.S.A. It was discredited by IMA in 1980, but stayed in gemology | Meru sapphire | Tanjeloffite, after the researcher D. Tanjeloff | Sapphire-zoisite.

Thulite, after Thule, old name of Norway | Rosaline, after its color | Unionite, after the discovery location near Unionville, Pennsylvania, the U.S.A., obs. | Manganese zoisite, after the content of MnO up to 0,5%.

Ornamental rocks – Anyolite, after its color, from “anyo” – green, Masai language, Tanzania, where it was found | Masai anyolite | Saussurite jade, after Swiss researcher O.B. Saussure | Nevada lapis, after the discovery location in Nevada, the U.S.A.

Quality improvement and cut gems. Annealed to 650°C rose zoisite, because of admixture of vanadium (V3+), becomes light blue, yellow-green one under 380-500°C becomes blue, and greenish-blue tanzanite with brownish and yellowish tones under 700°C becomes much more blue and violet dichroism is displayed in it. The most valuable variety of zoisite for faceting is tanzanite. The jewelry firm of Tiffany & Company in the U.S.A. made its popular as a new gemstone. It made a wonderful adornment with tanzanite for the film-star Elisabeth Taylor – a unique necklace with five large faceted stones. The biggest faceted tanzanite, 220 ct., is kept in a private collection, and in the Smiths. Inst., Wash. there is a pure blue faceted stone, 122.7 ct., for which more than $50,000 were played. Also there is a cabochon with the effect of cat’s-eye, 18.2 ct. and faceting tanzanite 12.11 ct. in platinum ring. Because of flakes inclusions of graphite in tanzanite, it should be faceted taking into account their orientation. Zoisite as it is – as a variety zoisite cat’s-eye, and also thulite and anyolite are processed in high cabochons.

Similar Gemstones & Imitations. Zoisite looks like epidote and pumpellyite; thulite – like rhodonite; chrome-zoisite – like jadeite, tanzanite – like sapphire, dumortierite, cordierite and spinel. Because of the popularity of tanzanite its imitations appeared – from gallium-phosphate glass and polycrystalline glass on the quartz base. Another imitation is synthetic corundum, synthetic spinel, as well as doublets from glass with upper part from tanzanite or from colorless synthetic spinel, glued with blue essence in the color of tanzanite; triplets of beryl or Mashishe beryl. Recent years, as an imitation of tanzanite they often use blue synthetic garnets under the tradename tanvanite, or purple coranite, or blue coranite. The newest imitation is synthetic forsterite – tanzanion.

Clinozoisite (Klinozoisit—Clinozoisite— линоцоизит) (Weinschenk, E. 1896). The name reflects its monoclinic symmetry and zoisite composition. Silicate – Ca2AlAl2[O|OH|SiO4|Si2O7], subclass diorthosilicates, the group of epidote, monoclinic system. Hardness 6.5. Density 3.2-3.4. Cleavage in one direction. Glass luster. Synonyms – aluminum epidote or clinoepidote because of the similarity with epidote and zoisite. It is found as columnar crystals, fibrous aggregates and grained masses. Transparent to translucent. Color: grayish-white, colorless, yellow, green, rose to raspberry-red. Color is often zonal; green hue depends on the admixture of chromium (Cr3+). Findings of large crystals are rare. It is found at deposits of metamorphic genesis. In Russia ornamental greenish clinozoisite in the South Urals, at the Kyshtym deposit is known. In the Subpolar Urals, it was found in the form of needle inclusions in crystals of rock crystal – clinozoisite cat’s-eye at the deposits Dodo and Puiva. In Norway, red clinozoisite at the iron ore Klodeberg deposit, near Arendal, was extracted. In the Radoy Is., to the north from Bergen, its crystals reached 6 cm. long. In Bulgaria, they discovered rose clinozoisite in the Central Rodopy Mts., near Chepelare; in Kenya – large crystals of gray-green and rose color; and in Madagascar – grayish-green crystals. In the U.S.A. in Vermont gem-quality brownish columnar crystals of clinozoisite up to 10 cm. in the Belvidere Mt. quarry, Orleans Co., were found. In California, massive ornamental material was discovered in the Los Angeles Co.; and in Nevada – in the Pershing Co. In Canada its findings are known at the Timmons deposit, Ontario. In Mexico, in the Baja California State, at the deposits Los Gavilanes and La Olivia occur transparent crystals of clinozoisite up to 3 cm. From them faceted stones up to 20 ct. were made. In the Sonora State the best clinozoisite, available for faceting, was found at the Alamos deposit. In faceted form stones are not more than 5 ct. In the Museum of Calgary, Canada, there is a brownish faceted clinozoisite from Iran 7.3 ct. in mass.

SynonymPistacite (pistazite), from Gk. “pistaxia” – pistachio, after its color.

 

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