月布ベントナイト鉱床における川向坑産ベントナイトと梅ノ木田坑産ベントナイトの鉱物学的比較

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Characterization of the Kawamukai (KB) and Umenokida (UB) bentonites from the Tsukinuno bentonite mines were investigated by XRD analysis, XRF analysis, ICP-MS, petrography, SEM, AFM, and surface area determination by the N_2-BET method. XRD analyses and petrography identified quartz, feldspar, zeolite facies, calcite, and montmorillonite in the Tsukinuno bentonite. The zeolite facies in KB and UB are analcime and clinoptilolite, respectively. The Mg/(Ca+Mg) ratio of calcite based on ICP-MS in KB is higher than that in UB. These results suggest that KB has undergone a higher alteration than UB. Since no heat source such as an igneous intrusion has been reported to affect the bentonite deposits, the difference in the degree of alteration can be attributed to the effective stress applied on the deposits during folding. This is supported by the higher angle of deformation found in the KB than in UB. The layer charge distribution in montmorillonite from both bentonites indicates a bimodal distribution. Mean layer charge of Kawamukai-montmorillonite (KM) is 0.31 esu/half unit cell, which is slightly higher than Umenokida-montmorillonite (0. 29 esu/half unit cell). However, this difference in mean layer charges does not affect expandability largely. Thickness of both montmorillonite layers (i.e. KM and UM) determined with AFM is close to the height of a single hydrated montmorillonite layer. The ab dimension of UM is bigger than that of KM. This results in a large difference in the edge surface area per unit mass for UM and KM. Since the edge surface areas are more reactive, differences in physical and chemical properties such as adsorptive ability and permittivity would arise for the two bentonites.
日本粘土学会の論文
2004-12-16

月布ベントナイト鉱床における川向坑産ベントナイトと梅ノ木田坑産ベントナイトの鉱物学的比較

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