Avogadrit

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Avogadrit
Ferruccite, Avogadrite - Vesuvius, Italia.jpg
Ferruccite (white) on Avogadrite (yellowish brown) from Vesuvius , Italy
(image width: 5 mm)
General and classification
chemical formula (K, Cs) [BF 4 ]
Mineral class
(and possibly department) 		Halides
System no. to Strunz
and to Dana 		3.CA.10 ( 8th edition : III / B.01)
02/11/02/01
Crystallographic Data
Crystal system orthorhombic
Crystal class ; symbol orthorhombic-dipyramidal; 2 / m 2 / m 2 / m
Physical Properties
Mohs hardness not defined
Density (g / cm 3 ) calculated: 2.507 to 3.305
Cleavage Please complete!
colour colorless, white, yellowish, reddish
Line color White
transparency transparent to translucent
shine Glass gloss to fat gloss
Crystal optics
Refractive indices n α  = 1.324
n β  = 1.325
n γ  = 1.325
Birefringence δ = 0.001
Optical character biaxial negative
Axis angle 2V = measured: 75 °; calculated: 58 °

Avogadrite 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) [BF 4 ], is thus seen a chemically potassium - tetrafluoroborate , with small proportions of potassium by cesium represented ( substituted may be).

Avogadrit only develops microscopic, octahedral, tabular crystals and thin, crusty coatings that are either colorless to white or yellowish to reddish due to foreign admixtures.

Etymology and history

Avogadrite was first discovered in 1926 on Vesuvius in Italy and described by Ferruccio Zambonini (1880–1932), who named the mineral after the famous Italian physicist and chemist Amadeo Avogadro (1776–1856).

classification

In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the Avogadrite belonged to the mineral class of "halides" and there to the division of "anhydrous double halides", where it formed an independent group with barberite and ferruccite .

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also assigns Avogadrite to the “halides” class, but in the “complex halides” department. This division is also further subdivided according to the crystal structure, so that the mineral can be found according to its structure in the sub-division of "Borofluoride", where it only forms the unnamed group 3.CA.10 together with Barberiite .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the Avogadrite to the class of "halides" and there in the department of "complex halides - aluminum fluorides". Here he is the only member of the unnamed group 02/11/02 within the subdivision of " Complex halides (and aluminum fluorides) with the general composition (A) m B (X) 4 ".

Crystal structure

Avogadrit crystallizes orthorhombically in the space group Pnma with the lattice parameters a  = 8.66  Å ; b  = 5.48 Å and c  = 7.03 Å as well as 4 formula units per unit cell .

properties

Avogadrit is slightly soluble in water, which therefore takes on a bitter taste.

Modifications and varieties

Above 273 ° C, Avogadrit converts its crystal system into the cubic modification .

Education and Locations

Avogadrit is formed by direct crystallization from the volcanic gases ( sublimation ) of the active fumaroles . Accompanying minerals include sassolin , malladrite and hieratite .

In addition to its type locality in Italy , the mineral could also be found worldwide on the west side of the Valle del Gigante between Monte Somma and Vesuvius (Atrio del Cavallo) and on the “La Fossa crater” on the Sicilian island of Vulcano . Avogadrit was also discovered in the Kamchatka Oblast in Russia.

See also

Web links

Commons : Avogadrite  - collection of images, videos and audio files

Individual evidence

  1. ^ A b c Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  160 .
  2. ↑ a b Webmineral - Avogadrite (English)
  3. ↑ a b c Avogadrite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 67.2 kB )
  4. ↑ a b c Mindat - Avogadrite (English)
  5. ↑ Centro Musei delle Scienze Naturali - Ferruccio Zambonini (Italian)
  6. ↑ Find location list for Avogadrite in the Mineralienatlas and Mindat