Modes of occurrence and mineralogy of mica clay minerals in the Hiroshima and the San'in granitic complexes

The differencies in modes of occurrence and mineralogical habites for mica clay minerals constituting clay veins in the Hiroshima and the San'in granitic complexes have been examined by X-ray powder diffraction, DTA, electron microscopic observation and pH method. Mica clay minerals in the Hiroshima granitic complexes: The clay veins consist of mica clay minerals with an accessories of kaolin minerals and montmorillonite. The mica clay mineral was identified to be 1 Md polytype and were poorly crystallized crystal. The Al/Fe+Mg ratios in octahedral positions of the mica minerals is lower than that of the ones from the San'in granitic complexes. Most DTA curves show double endothermic peaks reduced to the main dehydroxylation : one of the peaks appears at about 500°C and the other is between 650-700°C. Those crystals consist of thin irregular plate and elongated-tabular. The abrasion pH value suggests that the minerals was formed under acidic condition. Mica clay minerals in the San'in granitic complexes: The clay veins consist of mica clay minerals with an accessories of chlorite, kaolin minerals and montmorillonite. Mica clay minerals are 2M1, 1M and 1 Md polytypes and are well crystallized crystals. The Al/Fe+Mg ratios for most specimens are higher than that of the mica minerals from Hiroshima granitic complexes. The main dehydroxylation reaction of most specimens occurs between 650-700°C. Some hexagonal plates with irregular plates and elongated-tabular forms are observed. The abrasion pH values suggest that some of them were formed under the acidic conditions and the others the alkaline ones.