Hydrothermal alteration and formation of clay minerals.

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1. Geological studies of occurrence of clay minerals. The distribution and mineral associations of the alteration zones in Kuwanokizuru area, Ktuanoto Prefecture, Kawaragea and Doroyu areas, Akita Prefecture and Arita and Takarazuka areas, Hyogo Prefecture have been investigated by means of XRD, IR and chemical analysis.2. Crystal chemical studies of clay minerals. Li-tosudite from Tobe pottery stone, and Li-donbasite and tosudite from Echassidres granitic cupola have been examined by X-ray, chemical, thermal and infraed methods. Thermodynamic calculations assured that Li-donbasite possessed the stability field from 300 to 200ﾟC under acid conditions.3. Comparative studies of synthesis and the occurrence of clay minerals. (1) Smectites changes to mica, chlorite and some non-sheet silicates through interstratified mineral phases. The Al-rich samples were more reactive and changes to interstratified mineral phases at lower temperature than the Al-poore one. The formation temperature of interstratified minerals from beidellite is lower than that from montmorillonite. (2) Interstratified structures of intermediate illite/smectite products in the smectite illitization are distinguished from differences in permeability and porosity of original rocks. There are two distinct mechanisms of smectite illitization. (1) dissolution-growth dominant process. (2) Cation-substitution dominant process.4. New analytical methods of clay minerals. Chemical compositions of clay minerals were analyzed by analytical transmission electron microscope and compared with their bulk compositions measured by wet chemical analysis. Experimental factors such as, acceleration of voltage, dead time of detector, incident electron beam current, damage of specimen by an incident electron bean and contamination of specimen, should be given greater attention to get a more reliable result of quantitative chemical analysis of thin section specimen.