Stacking Order in a K/Mg Interstratified Vermiculite from Malawi

Abstract

Abstract--The stacking order of a bi-ionic K/Mg vermiculite from Malawi (Nyasaland), has been determined from Weissenberg data. The sample corresponds to a K/Mg interstratified vermiculite containing 50% K layers (dK = 1.01 rim) and 50% Mg layers with two layers of water (dM~ = 1.44 nm). The observed intensities along (0, 0), (h, 0), (0, k) and (1, k) reciprocal rods were compared to the calculated intensities given by model defect structures. It was found that: 1) The (h, 0), (0, k) and (1, k) rods reveal the interstratification phenomenon which was previously observed on the (0, 0) rod; 2) The exchange of Mg by K does not occur randomly in a single interlayer, but occurs in interlayer domains sufficiently extensive to allow the reorganisation of the layer stacking and development of the ordered K-vermiculite structure from the semi-ordered structure characteristic of magnesium vermiculites; 3) For this sample, the interlayer water of the Mg phase occurs in two coexisting configurations; one configuration has water molecules forming octahedral coordination around the Mg 2+, the other has water which is not linked to the Mg 2+ cation forming two planes.

Evolution of Benzylammonium-Vermiculite and Ornithine-Vermiculite Intercalates

“…The translations along X and Z are always unequivocal (-a/3 and d001). For semi-ordered stacks, the reciprocal space cannot be described by a set of hk/ reciprocal spots (b, k, l integers) but by modulated reciprocal rods (h, k) with a continuous variation of intensity along the rods that depends on the nature of the two-dimensional structural units and the way they are stacked (Mering 1949;Guinier 1964;de la Calle et al 1993). The rods are cylinders of infinite length with a small basal area centered on the hk nodes of the reciprocal lattice of the two dimensional structural units and perpendicular to the plane of this lattice.…”