抄録
The relation between sedimentary enviroments and clay minerals as wethering products of the Shimosueyoshi-Loam beds in the South Kanto district was examined by powder X-ray diffraction, DTA, CEC, TEM and chemical analyses of clay minerals and associated interstitial water. Some differencies were found in the particle shapes and stabilities of interlayer water of halloysites between in aqueous and aeolian tephra beds. Particle shape of halloysite in aqueous tephra beds is irregular shaped thin plate which is different from usual spheroidal and/or tubular shapes in aeolian tephra beds, and interlayer water of these platy halloysite was found to be more unstable than the others. This mineral may correspond with halloysite and metahalloysite mixde-layered mineral whith has been reported by Kurabayashi and Tsuchiya (1965). However, it shows only 10Å basal reflection and does not show 7Å one in the powder X-ray diffractogram under relative humidity of 100%, it was concluded to be halloysite 10Å mineral though having very unstable interlayer water. SiO2 concentrations of interstitial water associated with this platy halloysite are found to be apparently higher than those with spheroidal and/or tubular ones in aeolian tephra beds.
In the stability diagram of CaO (Na2O)-SiO2-Al2O3-H2O system, the data of aeolian tephra beds are plotted within the stability field of kaolinite, but those of aqueous tephra beds are plotted on the boundary of those between kaolinite and montmorillonite. It was then considered that a unipue sedimentary environment having a high SiO2 concentration of interstitial water may strongly affect the formation of this platy halloysite.
