Abstract
Clay minerals in a calcareous paddy soil have been investigated. The soil is an alluvium developed on transported sediments of weathering products of tertiary sedimental rocks in Miyagi Prefecture. The soil is somewhat impermeable, and its groud water is high (about 50 cm depth). The subsoil is highly alkaline (pH 8.2) and soft Ca-concreations are scattered in the layer of 40〜50 cm depth from the surface. Clays finer than 2.0μ were collected by sedimentation from surface and subsoil layer (30〜40 cm) and the clay portion were fractioned through centrifuge into several portions according to grain sizes. Each fraction was analyzed chemicaly, and the finest (0.2μ>) was investigated through electronmicrographs. From the analytical results, the coarse fractions are considered mainly "degraded illite" with some quartzs and the fractions between 0.2μ and 2.0μ may consist of nontronite and degraded illite, but the finest portions (0.2μ>) are the clay minerals of nontronite type resembling to both of beidellite and illite in some respects. The shapes of electronmicrographs, of clays (0.2μ>), which are considered to be nontronite by the authors, show irregular thin flakes like that of illites or Fe-montmorillonite and beidellites. A few interesting crystals, as shown in Fig 2 and 3,are found in the fractions of diameters between 0.2μ and 2.0μ. Although the former cube-like crystal is not identified, on concerning to the latter it may be suggested that there would be a possibility of existance and formation of hydrous calcium silicate group such as afwillite owing to the speciality of the soil conditions here studied.
