スメクタイトのイライト化に伴う膨張層の変化

抄録

The expansion properties of expandable layer in illite/smectite randomly interstratihed clay minerals (I/S) occurring in diagenetic alteration have been directly evaluated by behavior tests (expansion tests) using X-ray diffractometry. The behavior tests have been performed after following preparations : (1) ethylene glycol solvation ; (2) K-saturation and ethylene glycol solvation ; (3) Li-saturation, heating and glycerol solvation (Greene-Kelly test). The results of behavior tests for glycolated samples (unsaturated and K-saturated samples) suggest that smectite layer in I/S convert into high-charged one with increasing percentage of illite layer (I%). The results of Greene-Kelly test indicate that the expandable layer in I/S at early stage of illitization possesses both tetrahedral and octahedral charges, and that the amount of smectite layers having tetrahedral charge decrease with increasing I%. From the results of Greene-Kelly test, it is considered that the smectite layers having tetrahedral charge convert into illite layer selectively. The results of these behavior tests suggest that tetrahedral substitution of smectite layer is more effective in the illitization process than increasing the total layer charge.