Crystal Structures of Rb- and Ag-Substituted Forms of Natural Zeolite Amicite

Abstract

Abstract The crystal structures of ion-exchange products of the zeolite-group mineral amicite from Khibiny Alkaline Massif with silver and rubidium salts have been studied. The investigated samples are monoclinic (sp. gr. P 2 1 and I 2/ a ); their crystallochemical formulas ( Z = 1) are Ag 8 (Al 8 Si 8 O 32 ) ⋅ 10.6H 2 O and K 0.4 Na 0.7 Rb 6.9 (Al 8 Si 8 O 32 ) ⋅ 4.5H 2 O; the unit cell parameters are a = 9.272(2) and 10.043(2) Å, b = 9.997(2) and 9.748(2) Å, c = 10.380(3) and 10.265(2) Å, β = 90.821(8)° and 90.09(3)°, V = 962.0(4) and 1005.0(3) Å 3 , respectively. In the Ag-amicite structure, 22 partially occupied sites of the extra-framework components (Ag and H 2 O) are localized. In the Rb-amicite structure, most of rubidium atoms are located in two sites with the occupancies of 0.414(6) and 0.389(5). The cross-sectional areas of the zeolite channels are 3.5 × 4.5 and 2.3\xa0× 6.3 Å 2 for Ag-amicite and 3.0 × 4.3 and 3.0 × 3.9 Å 2 for Rb-amicite.