泥質片岩風化殻中のバーミキュライトとその起源

概要

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Vermiculite, 14.8Å in basal spacing, was found at a deep part of thick weathering crust of pelitic schist which is destributed in Higashi-ku, Fukuoka City, Southwest Japan. It has main characteristics of true vermiculite, not Al interlayer vermiculite (or 14Å intergrade) which is often found at the upper part of weathering crust or soils; the basal spacing easily collapses to 10.5Å after NH_4NO_3 treatment, not expands after ethylene glycol treatment, and does not gradually shift with increasing temperature. It shifts to 9.95Å at 300℃, 9.45Å at 500℃, 9.41Å at 800℃ and disappears at 900℃ with heat treatment. The 060 reflection and the chemical data by EPMA show that the vermiculite is tri-octahedral type and rich in iron. It cannot be denied that the vermiculite is derived from tri-octahedral mineral such as chlorite, but the probability is that it comes from phengite which is di-octachedral mineral. It seems that the vermiculite was formed in a process of deep weathering of the pelitic schist at the previous stage of the formation of the recent landforms.
日本粘土学会の論文
1998-03-31