Afghanite
- IMA 1967-041
- (Na, K) 22Ca10 ( Si24Al24 ) O96 (SO4) 6Cl6
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) 22Ca10 ( Si24Al24 ) O96 (SO4) 6Cl6. The values given in the parentheses elements sodium and potassium may be doing in the formula each represent each other (substitution, Diadochie ), but are always in the same proportions to the other components of the mineral. Chemically, Afghanite so that a sodium - potassium -calcium aluminosilicate with additional chlorine and sulfate ( [ SO4 ] 2 -) anions. Structurally, it belongs to the framework silicates.
Afghanite is transparent and developed thick - to dünntafelige, strip-shaped crystals with glass-like shine, but is also found in the form of rounded grains. Its color varies between light and dark blue, in thin layers, however, it is colorless.
Etymology and history
Afghanite was first discovered described in the well known since ancient times lapis lazuli deposit Ladjuar Medam near Sar -e -Sang in Afghanistan and 1968 by P. Bariand, F. Cesbron and R. Giraud, who named the mineral after its discovery Afghanistan.
Classification
In the now outdated but still in use 8th edition of the mineral classification by Strunz the Afghanite belonged to the department of " framework silicates ( tectosilicates ) " where he, along with Bystrit, cancrinite, Cancrisilit, Davyn, Farneseit, Franz Init, Giuseppettit, Hydroxycancrinit, Liottit Marinellit, Mikrosommit, Pitiglianoit, Quadridavyn, Sacrofanit, Tounkit, Vishnevit and Wenkit the " cancrinite - series" with the system no. VIII/J.09 formed.
The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns the Afghanite in the fine already divided the department " framework silicates ( tectosilicates ) without zeolitic H2O" one. This is also further divided according to the possible presence of additional anions, so that the mineral is found according to its composition in the subsection " framework silicates ( tectosilicates ) with additional anions ," where it along with Alloriit, Balliranoit, Biachellait, Bystrit, cancrinite, Cancrisilit, Davyn, Fantappièit, Farneseit, Franz Init, Giuseppettit, Hydroxycancrinit, Kyanoxalith (IMA 2008-041 ), Liottit, Marinellit, Mikrosommit, Pitiglianoit, Quadridavyn, Sacrofanit, Tounkit and Vishnevit the " Cancrinitgruppe " with the system no. 9.FB.05 forms.
The mainly common in English-speaking classification of minerals according to Dana assigns the Afghanite in the class of " silicates and Germanates " and then in the Department of: a " framework silicates Al- Si lattice ". Here he is in the " Cancrinitgruppe " with the system no. 76.02.05 within the subdivision " framework silicates: Al- Si lattice, feldspar and related species " to find.
Education and Locations
Be found Afghanite At its type locality Sar -e -Sang in the form of thin veins within there also discovered Lazurite crystals. Besides Lasurit occur among others still calcite, diopside, nepheline, olivine, phlogopite, pyrite, sodalite and vesuvianite.
The only known locality in Germany is the Ettringer Bellerberg at Ettringen in the Eifel region of Rhineland- Palatinate.
Other localities include the Monte Somma, Pitigliano and several points Fund in the provinces of Rome and Viterbo in Italy; Kimmirut in Canada; the Malaya Bystraya River Valley in Rajon Slyudiyanka near Lake Baikal in Russia; the Lasuritlagerstätte the river Lyadzhvardara in the Pamir Mountains in Tajikistan and the " Edwards Mine" at " Edwards " in the St. Lawrence County ( New York) in the U.S..
Crystal structure
For a different composition of Afghanite with the formula (Na, K, Ca) 6Ca2 [ (SO4, CO3 ) 2 | (Cl, OH) 2 | (Al, SiO 4 ) 6] · nH2O has a trigonal crystal structure in the space group P31c ( space group no. 163) with the lattice parameters a = 12.77 Å and c = 21.35 Å and four formula units per unit cell determined.