Weathering of Montmorillonite in Soils

Abstract

In the last decade much effort has been exerted by a number of Japanese soil workers to identify the clay minerals of their soils. Generally speaking, results of this work indicate Japanese soils should be said to be halloysitic, but some soils are montmorillonitic, and some others are allophanic. Montmorillonites were identified in marine alluvial soils¹⁾²⁾, paddy soils^3)4)5)6), extremely strong acid soils 1 Toshio HIGASHI: Clay minerals and base status of strongly acid soils (unpublished). View all notes , and others^{7)8)9)10)11)12)13)}. Soil montmorillonites have arrested attention in regard to the characteristic behavior of high cation adsorption and expansion in water from the point of view of soil productivity. Routine works for identification of clay minerals have disclosed soil montmorillonites different in degrees from a typical montmorillonite as that in Wyoming bentonite. X-ray diffraction patterns have revealed low intensity of (001) reflections ; differential thermograms have represented development of an endothermic peak at about 550°C accompanying ecay of the peak at 700°C, and chemical compositions have shown admission of Al and OH ions. It suggests that montmorillonites are subjected to weathering in environment of low base status. The previous paper dealt in the problem of montmorillonite-weathering in tuffaceous shales under severe leaching, and demonstrated changes of the crystallite by weathering. However, the degree of weathering of the samples used in that work was not great even in most weathered one, and, further, their montmorillonites contained an appreciable amount of illitic lattice as an integrant. The latter fact would obscure to some extent the montmorillonite structure from X-ray examination.