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Russian Gemstones Encyclopedia

Vladimir Bukanov. Russian Gemstones Encyclopedia

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PETALITE


PETALITE (Petalit—Pétalite—ѕеталит) (d’Andrada J.B., 1800), from Gk. “petalo” – a petal, after its leaf-like cleavage.

Composition & Properties. Silicate – Li[4]Al[4][Si4O10], subclass of carcass, monoclinic system. Hardness 6.5. Density 2.4. Glass luster, nacre one along the cleavage plane. Cleavage in one direction. Petalite usually forms solid leaf-like masses, rarely it is found in the shape of thick-table or short-columnar crystals. Color: white, colorless, gray, yellow, sometimes reddish, rose or greenish-white. Transparent to translucent.

Deposits. Petalite is a rare mineral of granite pegmatites. In Russia, separate findings of petalite are known in the Middle Urals, at the mines of Lipovka. In the Northern Caucasus, its crystals were found in the region of the glacier Amanauz; in East Transbaikalia – at the Zavitinskoye deposit. In East Kazakhstan, petalite in pegmatites at the Krasnyi Kordon deposit, near Asu Bulak, Kalbinskiy Ridge, was discovered. In Italy, on the Elba Is., petalite was found in pegmatites of the region of San Piero in Campo. In Afghanistan, at the Paprok deposit, Kunar Prov., petalite crystals up to 25 cm.; and in the Laghman Prov. transparent crystals are not more than 7 cm. were extracted. In Namibia, in the Karibib area large yellow, brown-rose and colorless transparent crystals, and as pink masses at Rubicon mine were found. In Western Australia, at the Mineral Lees-80 deposit, near Londonderry, colorless or light yellow petalite, available for faceting, were extracted. In the U.S.A., findings petalite crystals up to 20 cm. at Lander, Fremont Co. and at the Bonneville deposit, Wyoming, were registered. In Massachusetts – at the Bolton deposit; in California – at the San Diego Co.; in Maine – at the deposits Greenwood, Newry, and Harward Quarry. From rough material of these deposits they made faceted stones up to 2 ct. In Brazil, petalite forms large masses up to 100 tons of pure, without any admixtures at Maxixe mine, and rarely gem-quality crystals at the Urubu mine, near Arçuaí, Minas Gerais. When cut in cabochon, it displays sometimes the effect of cat’s-eye. In the same state, in pegmatites of the region of Itinga and at the Urubu deposit, together with other gemstones, they found large crystals of transparent petalite; and at the Maxixe mine they discovered large accumulation of solid aggregates of petalite up to 100 tons in mass.

Synonyms. Castorit, after the name of the mythological hero Castor | Lithite | Petalite prismatic spar.

Treatment. Ornamental massive rose petalite is available for cutting in translucent cabochons. Sometimes, with inclusions of analcime, it displays the effect of cat’s-eye in cabochon. The most part of faceted stones are colorless and looks like glass, and pale colored ones look like amblygonite. Usually, they are not more than 20 ct., rarely – up to 100 ct. In the Smiths. Inst., Wash., they expose a faceted colorless petalite in 55 ct. from Namibia. In the Museum of Calgary, Canada, there is a colorless petalite from Australia in 14.8 ct. The weight of the biggest processed stone, which is kept in a private collection, is 206 ct.

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