X-RAY-DIFFRACTION OF HYDRATED AND DEHYDRATED NACRITE STACKING MODES

X-ray diffraction based on the comparison of experimental and calculat ed powder profiles enabled the determination of the structural charact eristics of hydrated and dehydrated Tunisian nacrite. Using the concep t describing the structure of natural nacrite, the stacking mode of th e layers in the hydrated and dehydrated nacrite has been determined. T he hydrate is characterized by an 8.42 Angstrom basal distance; one wa ter molecule per Si2Al2O5(OH)(4) is intercalated in the interlamellar space, located above the vacant octahedral site of the layer at z = 6. 5 Angstrom and inserted inside the ditrigonal cavity of the tetrahedra l sheet of the upper layer. The dehydrated nacrite obtained by heating of the hydrate at 423 K has the same interlayer shift t = -0.35a as t he natural nacrite. Coherence domain sizes along c and in the nb plan e are the same as those in the hydrate but different from those of the natural mineral. After dehydration, 5% of the layers had an interlaye r shift similar to that obtained from the hydrate.