A SHORT-RANGE INTERACTION-MODEL APPLIED TO ILLITE SMECTITE MIXED-LAYER MINERALS/

We present a solid solution model, able to take into account short-ran ge interactions up to the third nearest neighbor. This model has been applied to illite/smectite mixed-layer clay minerals and tests the rel ative thermodynamic stability of each illite/smectite stacking sequenc e. The non-ideal energy terms have been calculated, showing a strong d ecrease of the interaction energy as the distance between elements gro ws, From Delta G(m) calculations the model predicts the following succ ession in TIS stacking sequences as X-i, tends to 1:R1, R2 and then R3 , This succession agrees well with some mineralogical observations in natural series.