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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

ALUNITE


ALUNITE (Alunit—Alunite—јлунит) (Beudant, F.S. 1824), from its composition, a contraction aluminite, alum.

Composition & Properties. Sulfate group – KAl3[(OH)6|(SiO4)2], trigonal system. Hardness 3.5-4. Density 2.6-2.8. Glass luster to pearl one. Cleavage in one direction. Fragile. Alunite is found as fine-grained, solid cryptocristalline masses. Translucent to non-transparent. Without admixtures the mineral is colorless, slightly yellowish. Its color is brownish, greenish, light bluish, not rarely it is spotty, which depends on admixtures. A solid, bright colored variety has high hardness because of quartz in their content; they are used as an ornamental stone. Light bluish copper alunite is used sometimes as imitation of turquoise.

Deposits. It is formed in volcano zones in the process of metasomatic transformation of rocks. It is found in hydrothermal veins and in zones of oxidation of ore deposits. In Russia, in the Amur Region there is the Burindinskoye deposit of ornamental alunite in the Magdagacha Dist. It is linked with secondary quartzites and on the space of 2 km.2 it is represented with lenses up to 200 m. long and 50 m. thick. In the Ukraine, there is a similar hydrothermal-metasomatic deposit – the Began’skoye in the Zakarpats’ka Region, near Berehove; and in Azerbaijan, near Dashkesan – the Zaglik deposit with multicolored massive alunite. In Uzbekistan, at the Ak-Tash deposit, to the north from Tashkent, they find rose varieties of alunite. In Auminzatau, at the Auminza deposit, alunite is found as admixture in turquoise and they are processed together in cabochons. At the Gushsaiskoye deposit, fine stripes are observed in alunite because of the alternation ferruginous and white layers. Important deposit in Western Australia is by Campion Lake. In the U.S.A., in the Utah State, there is a vein type of deposits with pure alunite. Thickness of veins at such deposit reached 18 m. in the bulges, the length was up to 100 m.

Synonyms. Alaunspar | Alumstone | Calafatite, after Spanish researcher J. Calafate Leon; from the Almeria deposit, Spain, discr. | Lowigite, obs. | Newtonite, after the discovery location near Newton, Arkansas, the U.S.A. | Alum ore | White alum ore | Aluminous spar.

Similarity. Alunite is hardly differs from kaolinite, it is similar with turquoise.

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