Alteration of Plagioclase in Granite during Weathering

KITAGAWA Ryuji

KAKITANI Satoru

Journal of science of the Hiroshima University. Series C, Geology and mineralogy

Secondary minerals of plagioclase in spheroidally weathered granite of the Seranishi-cho, Hiroshima Prefecture, Japan have been examined by the technique of X-ray diffraction, X-ray fluorescence, DTA, TGA, pH measurements and electron microscopic observation. Spheroidally zoning of A, B and C owing to the difference of appearance at outcrop corresponds to the secondary mineral components, that is, allophane or allophane-like substance is found only in the zone C of core-part of granite and the zone B, metahalloysite and halloysite are predominant in the zones A and B that were intensely weathered parts, and kaolinite exists in the zones A and B, but lacks in the zone C. The crystallinity and grain-size of these kaolin minerals increase gradually from near central core-part toward the outer A zone. The probable al-terating sequence of plagioclase in the weathered granite of this district has been roughly assumed as follows:
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eng

HIROSHIMA UNIVERSITY

[ISSN] 0075-4374

[NCID] AA00706718