Natural and monoionic aliettite: hydration and dehydration states

The dehydration of an interstratified talc-trioctahedral smectite mineral (aliettite) from Monte Chiaro, Taro Valley, Italy, saturated by Na, K, Rb, Cs, Mg, Ca, Sr, Ba and NH4 cations, was studied by X-ray powder diffraction and thermal analysis, under different conditions of temperature and relative humidity. Both in the natural and exchanged states the mineral exhibited several orders of basal reflections and, to varying relative humidity (P/Po) and temperature (T) conditions, behaved like a smectite except that: (i) the c-dimension was not very sensitive to relative humidity increase; (ii) the closest packing was for T > 400~ the collapsed state being reached gradually as Tincreased and an inverse trend was apparent between 20 ~ and 300~ (iii) the endothermic reactions at T = 400~ and T = 600~ appeared to be affected by the exchange treatment. The experimental data are consistent with a structural model in which it is possible to distinguish layers containing a patchwork of talc and smectite domains: the patchworks are superposed to make a regular alternation of the two domains.