The crystal structure of paranatrolite

Abstract

Paranatrolite from the Khibiny massif, Kola Peninsula, Russia, Na 1.88 K 0.22 Ca 0.06 [Al 2.24 Si 2.76 O 10 ].3.1H 2 O, is monoclinic (space group Cc, Z = 4). For better comparison of this mineral with the related structure of natrolite, we have selected a pseudoorthorhombic setting in F1d1 ( a = 18.971(4), b = 19.204(3), c = 6.5952(12) A, β = 91.601(18)°, Z = 8). The dominant Na+ cations are situated near the sodium positions in the natrolite structure. Additional positions occupied by K+ are located in the eight-membered rings. H 2 O molecules are located in four independent positions, two being occupied statistically. The Na-polyhedra correspond to distorted NaO 3 (H 2 O) 3 octahedra forming chains along the c axis by sharing common H 2 O-H 2 O edges and H 2 O vertices. The availability of potassium in the structure results in two configurations for the coordination environment of Na+.