s
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

PHENAKITE


PHENAKITE (Phenakit—Phénakite—‘енакит) (Nordenskiöld, N. 1833), from Gk. “phenax” – a deceiver, because it was easily taken for quartz.

Composition & Properties. Silicate – Be2[4][SiO4], subclass orthosilicates, trigonal system. Hardness 7.5-8. Density 2.9-3. Glass luster to greasy one. Cleavage in one direction. Fragile. It is found in the form of transparent crystals of short-columnar and isometric shape, up to 20 cm. in cross-section. Separate half-transparent crystals reach 3 kg. in mass. Sometimes, crystals form radial-rayed aggregates. Color: colorless, sometimes pale wine-yellow, rose-red, more rarely greenish-light blue or brownish. The color is unstable, it is weakened in the light. There are such inclusions in it as needle crystals of sulfide of aikinite and flakes of muscovite. Inclusions of phenakite in emerald are a typical sign of its artificial origin.

Deposits. It is found in pegmatites, greisens, and metamorphic schists. In Russia, phenakite was discovered in the Middle Urals by Ya.V. Kokovin (1787-1840) at Izumrudnye Kopi (Emerald Mines) in 1833; it has been called kokovinite for some time. It was found in significant volume, and during the first 30 years after the finding they have extracted more than 82 kg. of phenakite, almost the same volume as those of alexandrite. When processed, phenakite sometimes displays the effect of cat’s-eye. One of the best samples of phenakite was a transparent crystal of the perfect shape, 18x15x12 cm. in size. The biggest crystal, 22x15x8 cm. in size, is kept in the collection of the Mining Museum, SPb., and in the Ural Geological Museum, Yekaterinburg, there is a crystals 7 kg. in mass. In 1867, at the World Exhibition in Paris, a faceted phenakite from the Urals was sent, 2.2 cm. in diameter, thick-yellow with rose tone. After a pair of month, it has lost its color completely. Recently, phenakite was found together with chrysoberyl at the Lipovka mine. In the South Urals, rose-red phenakite was discovered in alkali pegmatites of the Ilmeny Mts. in 1844. In the East Sayan Mts., they found phenakite at the Snezhnoye deposit; in Buryatia Rep. – at the Yermakovka deposit in spherulites up to 3 cm.; in pegmatites of Transbaikalia – at the Adun Chilon deposit; in the Primorskiy Region – at the Voznesenskoye and Yaroslavskoye deposits.

In the Ukraine, at the Volhynskoye deposit in the Zhitomir Region, phenakite was found in pegmatites in the form of crystals up to 3 cm. in cross-section. In Central Kazakhstan, it is known at the Oratau deposit, near Agadyr; and at a deposit in the region of Qarqaraly (form. Karkaralinsk); and in Kyrgyzstan – at the Kalisai deposit, to the east from Bishkek. In the southern part of Norway, crystals of phenakite up to 30x5 cm. at the Kragerø deposit, Telemark, were extracted. In Austria, at the Habachtal deposit, transparent crystals of light orange phenakite up to 10 cm. in cross-section were extracted together with emerald. They made faceted stones from them, up to 12 ct. In alpine veins phenakite is represented with beautiful crystals up to 8 cm. in cross-section. It is occurring in Austria at the Legbachrinne deposit, Salzburg; in Switzerland – at the Rekingen deposit, Wallis; in Poland – at Strzegom; and in France – at Framont mine, Haute-Saône, Franche-Comté.

On Madagascar, at the Anjanabonoina deposit near Betafo, in pegmatites, they found rather large crystals of red phenakite colored in zones. One of such crystals, 10.8x6.5x5 cm. in size, is exhibited in the École Nation. Supér. Min., Paris. Findings of small crystals of phenakite are known in Namibia, at the Spitzkopje deposit, near Usakos; as well as in Tanzania – to the east from Mpwa Mpwa, Kiswaiti Mts. On Sri Lanka, from a placer, larges crystal phenakite in the form of a pebble up to 1,470 ct. were extracted. They made a faceted stone from it, 569 ct., which is kept in the Smiths. Inst., Wash. now. In Brazil, phenakite was discovered in the early of 1880s in pegmatite of Caraca Hill, near São Miguel de Piracicaba, Minas Gerais, where they extracted 13 tons of this minerals. Its rounded, transparent, colored pale red crystals reached 10 cm. in cross-section. In 1983, in the same state, phenakite was extracted at the Pica Pao deposit, near Três Barras, and at the Mimoso do Sol deposit, Espírito Santo State. Transparent crystals of phenakite were heir about 2 cm, rarely they reached the size of 6 cm. In Bahia State, phenakite was extracted as additional material at the emerald Socotó deposit, near Campo Formoso, where its half-transparent crystals were not more than 10 m. long. In the U.S.A., gem-quality crystals of phenakite up to 4 cm. were found at the deposits Mt. Antero, Chaffee Co., and Pikes Peak massif, El Paso Co., Colorado. In California, such crystals at the Pala deposit are found; in Maine State – at the Lords Hill deposit; and in New Hampshire from colorless crystals stones up to 37x25x12 mm. up to 114.2 ct. made faceted.

Synonyms. Ural diamond | Rhombohedral emerald | Kokovinite, after Ya.V. Kokovin, a discoverer of this mineral, a manager of the Yekaterinburg lapidary factory, Russia | Phenacite.

Treatment. It is in the brilliant-cut of faceting, because in this case its color is better displayed; and also with the step pattern of faceting. Stones without any defects are usually not more than 5 ct., bigger ones up to 10 ct. have inclusions and cracks. Under irradiation phenakite becomes yellowish-brown.

Synthesis. Synthetic phenakite is received with the method of flux from a solution in melt. Under this procedure, because of the admixture of vanadium, light blue or blue-green zonal color is received. Manufacturing of synthetic phenakite has been organized in Russia.

Similarity & Imitations. Phenakite looks like diamond, beryllonite, cerussite, danburite, noble beryl, rock crystal, and topaz. In jewelry they sometimes use synthetic phenakite for imitation of brilliants.

Search