Amorphous materials in a spodosol: Some mineralogical and chemical properties

Abstract

The amorphous soil colloids present in spodosols were separated by a pH 3.7 acid dispersion technique instead of the conventional alkali dispersion procedure. The separated fraction contained 54–64% of amorphous material, the rest being crystalline components. The procedure, however, recovered only 14–33% of the clay obtained by the normal procedure, but appears to be a promising method for obtaining a concentrate of the amorphous material for the study of their properties. The B 2ir horizon of Onaway sandy loam, a spodosol, contained relatively greater amounts of amorphous material than the other horizons in the same profile. The silica-sesquioxide ratio of the amorphous colloid varied from 1.25 to 1.71 and was thus different from most allophanes of volcanic origin. About 1.5–2.0% of Fe 2O 3 were associated with the amorphous fraction and were not removed by an initial dithionite-citrate extraction. The amorphous colloid fraction contained 15–22% of OH water which varied in the different horizons. The cation exchange capacity of the amorphous fraction varied from 66–95 me/100 g and followed the same trend as silica-sesquioxide ratio. Amorphous material fixed K up to 5 me/100 g of clay, and so in samples where large amounts of amorphous materials are present, this should be taken into consideration in the quantitative mineralogical analysis scheme.