Avogadrit is a very rarely occurring mineral from the mineral class of " halides ". It crystallizes in the orthorhombic crystal system with the chemical composition (K, Cs) [BF4 ] and developed only microscopic octahedral, tabular crystals and thin, crusty coatings that are either colorless to white or by foreign admixtures are yellowish to reddish.
Avogadrit is slightly soluble in water, which thus takes on a bitter taste.
Etymology and history
Was first discovered Avogadrit 1926 at Vesuvius in Italy and described by Ferruccio Zambonini ( 1890-1932 ), who named the mineral after the famous Italian physicist and chemist Amadeo Avogadro ( 1776-1856 ).
In the now outdated but still in use 8th edition of the mineral classification by Strunz the Avogadrit belonged to the mineral class of " halides " and then to the Department of " anhydrous Doppelhalogenide ", where he formed a distinct group with Barberiit and Ferruccit.
The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns the Avogadrit also in the class of " halides ", There, however, in the department of " complexes halides ". This department is also further divided according to the crystal structure, so that the mineral is found in accordance with its construction in the subdivision of " Borofluoride " where it only forms the unnamed group 3.CA.10 together with Barberiit.
The mainly common in English-speaking classification of minerals according to Dana assigns the Avogadrit in the class of " halides " and then in the Department of - a "Complex halides of aluminum fluorides ." Here he is the only member of the unnamed group 11:02:02 within the sub-division of " complexes halides ( fluorides and aluminum ) with the general composition (A) mB (X ) 4".
Modifications and varieties
Above 273 ° C converts Avogadrit be crystal system in the cubic modification order.
Education and Locations
Avogadrit formed by direct crystallization from the volcanic gases ( sublimation ) of the active fumarole. Accompanying minerals include Sassolin, Malladrit and Hieratit.
Worldwide, the mineral is found on the Sicilian island of Vulcano except at its type locality in Italy or on the west side of the Valle del Gigante between the Monte Somma and Vesuvius ( Atrio del Cavallo ) and at " La Fossa crater ". In addition Avogadrit was discovered in the Kamchatka Oblast in Russia.
Avogadrit crystallizes in the orthorhombic space group Pnma with the lattice parameters a = 8.66 Å; b = 5.48 Å and c = 7.03 Å and four formula units per unit cell.