Chemical composition and some thermal data of eighteen allophanes from ando soils and weathered pumices

Abstract

The chemical composition, or rang of chemical composition, of allophane is not fully clear at present. Although many data have been published on chemical composition as well as on the other chemical and mineralogical properties of soil allophane, it seems that, in many cases, greater or smaller amounts of impurities such as free sesquihydroxides and crystalline minerals are included in the samples for analysis. There would be no guarantee, therefore, that these past data, especially the chemical composition data, accurately represent the properties of soil allophanes. The present author and Aomine (14) established early a method of separation of pure allophane from certain Ando soils and this threw light on the study of various properties, especially of chemical composition, of soil allophane. In the present study, the method was applied further to thirty-six samples of soil derived from volcanic ash (Ando soils) and pumice, and from eighteen samples of them the pure or nearly pure specimens of allophane were separated. The specimens separated were analysed for elemental composition and by differential thermal technique.