Afghanit

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Afghanit
Afghanite, pyrite, calcite 4.JPG
Afghanite (blue) with pyrite (gold-colored) on calcite from the type locality Sar-e-Sang , Afghanistan
General and classification
other names

IMA 1967-041

chemical formula (Na, K) 22 Ca 10 (Si 24 Al 24 ) O 96 (SO 4 ) 6 Cl 6
Mineral class
(and possibly department) 		Silicates and Germanates - framework silicates
System no. to Strunz
and to Dana 		9.FB.05 ( 8th edition : VIII / J.09)
76.02.05.01
Crystallographic Data
Crystal system trigonal
Crystal class ; symbol ditrigonal-scalenohedral; 3 2 / m
Room group (no.) P 3 1 c (No. 163)
Lattice parameters a  = 12.77  Å ; c  = 21.35 Å
Formula units Z  = 4
Physical Properties
Mohs hardness 5.5 to 6
Density (g / cm 3 ) measured: 2.55; calculated: 2.65
Cleavage completely according to {10 1 0}
Break ; Tenacity shell-like
colour light blue to dark blue, colorless in thin layers
Line color White
transparency transparent
shine Glass gloss
Crystal optics
Refractive indices n ω  = 1.523
n ε  = 1.529
Birefringence δ = 0.006
Optical character uniaxial positive

Afghanite is a rarely occurring mineral from the mineral class of " silicates and germanates ". It crystallizes in the trigonal crystal system with the chemical composition (Na, K) 22 Ca 10 (Si 24 Al 24 ) O 96 (SO 4 ) 6 Cl 6 . The elements sodium and potassium specified in round brackets can represent each other in the formula ( substitution , diadochie), but are always in the same proportion to the other components of the mineral. From a chemical point of view, afghanite is a sodium, potassium, calcium , aluminosilicate with additional chlorine and sulfate ([SO 4 ] 2− ) anions . Structurally it belongs to the framework silicates .

Afghanite is transparent and develops thick to thin tabular, strip-shaped crystals with a glass-like sheen , but is also found in the form of rounded grains . Its color varies between light and dark blue, but it is colorless in thin layers.

Etymology and history

Afghanit was first discovered in the already since ancient times known lapis lazuli - deposit Ladjuar Medam near Sar-e-Sang in Afghanistan and in 1968 by Pierre Bariand (* 1933), Fabien Cesbron and Roger Giraud described, designated the mineral after its discovery Afghanistan.

classification

In the meantime outdated, but still in use 8th edition of the mineral classification by Strunz of Afghanit belonged to the department of the " framework silicates (tectosilicates)" where he collaborated with Bystrit , Cancrinit , Cancrisilit , Davyn , Farneseit , Franz Init , Giuseppettit , Hydroxycancrinit , Liottit , Marinellit , Mikrosommit , Pitiglianoit , Quadridavyn , Sacrofanite , Tounkit , Vishnevite and Wenkit the "Cancrinit series" with the system no. VIII / J.09 formed.

The 9th edition of Strunz's mineral systematics, which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), classifies afghanite in the more finely subdivided division of “tectosilicates without zeolitic H 2 O”. This is further subdivided according to the possible presence of additional anions , so that the mineral can be found according to its composition in the sub-section “ Tectosilicates with additional anions”, where it can be found together with alloriite , balliranoite , biachellaite , bystrite, cancrinite, cancrisilite , Davyn, Fantappièit , Farneseit, Franzinit, Giuseppettit, Hydroxycancrinit, Kyanoxalith ( IMA 2008-041 ), Liottit, Marinellite, Mikrosommit, Pitiglianoit, Quadridavyn, Sacrofanit, Tounkit and Vishnevit the "cancrinite group" with the system no. 9.FB.05 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Afghanite to the class of "silicates and germanates" and there into the department of "framework silicates: Al-Si lattice". Here he is in the " Cancrinit group " with the system no. 76.02.05 can be found in the sub-section "Framework silicates: Al-Si lattices, feldspar representatives and related species".

Education and Locations

Afghanite crystal on calcite from Sar-e-Sang, Afghanistan (size: 35 mm)

At its type locality Sar-e-Sang, Afghanite was found in the form of thin veins within the lazurite crystals that were also discovered there . In addition to lazurite, calcite , diopside , nepheline , olivine , phlogopite , pyrite , sodalite and vesuvianite also occur.

As a rare mineral formation, Afghanite could only be detected at a few sites, with around 20 sites being known.

The only known site in Germany so far is the Ettringer Bellerberg near Ettringen in the Eifel in Rhineland-Palatinate.

Other sites include the Monte Somma , Pitigliano and several sites in the provinces of Rome and Viterbo in Italy; Kimmirut in Canada; the Malaya-Bystraya river valley in Slyudjanka district near Lake Baikal in Russia; the Lasuritlagerstätte the river Lyadzhvardara in the Pamir Mountains in Tajikistan and the "Edwards Mine" with "Edwards" in St. Lawrence County (New York) in the USA.

Crystal structure

For a different composition of Afghanite with the formula (Na, K, Ca) 6 Ca 2 [(SO 4 , CO 3 ) 2 | (Cl, OH) 2 | (Al, SiO 4 ) 6 ] · nH 2 O, a Trigonal crystal structure in the space group P 3 1 c (space group no. 163) with the lattice parameters a  = 12.77  Å and c  = 21.35 Å as well as four formula units per unit cell determined.

See also

literature

  • P. Bariand, F. Cesbron, R. Giraud: Une nonvelle espece minerale: L'afghanite de Sar – e – Sang, Badakhshan, Afghanistan – Comparaison avec les mineraux du groupe de la cancrinite , In: Bulletin de la Société Française de Minéralogie et de Cristallographie , Volume 91 (1968), pp. 34–42 ( PDF 590.2 kB )

Web links

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

Individual evidence

  1. ↑ a b IMA / CNMNC List of Mineral Names - Afghanite (PDF 1.3 MB)
  2. ^ 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.  709 .
  3. ↑ a b Afghanite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 73.7 kB )
  4. ^ Mindat - Afghanite
  5. ↑ Fabien Cesbron, Hélène Vachey: La bariandite, nouvel oxyde hydrate de vanadium (IV) et (V). In: Bulletin de la Société Française de Minéralogie et de Cristallographie. Volume 94 (1971), pp. 49-54 ( PDF 333.5 kB )
  6. Jump up ↑ Fabien P. Cesbron, Daria Ginderow, Roger Giraud, Pierre Pelisson, Francois Pillard: La nickelaustinite Ca (Ni, Zn) (AsO 4) (OH); nouvelle espece minerale du district cobalto-nickelifere de Bou-Azzer, Maroc. In: Canadian Mineralogist. Vol. 25, No. 3, 1987, pp. 401-407
  7. ↑ P. Bariand, F. Cesbron, R. Giraud: Une nonvelle espece minerale: L'afghanite de Sar – e – Sang, Badakhshan, Afghanistan – Comparaison avec les mineraux du groupe de la cancrinite , In: Bulletin de la Société Française de Minéralogie et de Cristallographie , Volume 91 (1968), pp. 34–42 ( PDF 590.2 kB )
  8. ↑ Mindat - Number of localities for Afghanite
  9. ↑ Find location list for Afghanite in the Mineralienatlas and Mindat