テフラおよびテフラ由来土壌中のアルミナ・シリカ・ミネラロイド

概要

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Hardened gel-like particles which are rich in alumina and silica were found in pores of volcanic glass in tephras and tephra-derived soils in Hokkaido. They are here named alumina-silica mineraloids because of the major chemical constituents. We investigated the mineraloids collected from 4 tephras at 5 sites. (1) The mineraloids were found in all the horizons studied. They are platy (circular, elliptical and rhombic) and non-platy (massive and spherical) in shape, and the platy shaped ones are dominant. Their average diameter is 109 μm, and the thickness of the platy type is 1/10〜1/15 of the major axis. (2) Clay mineral compsition of the mineraloids differs from that of clay fraction in the same horizon. It is simple and varies with the tephras; halloysite (7 Å), imogolite or a poorly-crystallized layer silicate mineral. (3) SiO_2 and Al_2O_3 contents of the mineraloids range 49〜57% and 29〜44%, respectively. (4) The mineraloids are assumed to be initial weathering products which were formed in the pores of pumice and volcanic glass by preciptation of the dissolved constituents of volcanic glass and other minerals.
日本ペドロジー学会の論文
1989-12-31