Nature and Distribution of Amorphous Aluminosilicates in Arid Soils of Western Rajasthan

The coarse and fine clays from selected horizons of ten arid zone soils were studied for the content and composition of amorphous aluminosilicates. Dune soil clays contained highest amount (8 to 15%) of amorphous aluminosilicates followed by interdune (3.5 to 15%), sandy alluvial plains (3 to 7%), and medium to fine textured alluvial plains (4 to 12%). The amorphous aluminosilicate content of fine clays was nearly twice that of the coarse ones. The SiO₂: Al₂O₃ molar ratio of the amorphous material ranged from 1.2 to 3.5 in coarse clays and from 3.0 to 5.8 in fine clays. Amorphous aluminosilicates in coarse clays were composed of tetrahedral [Si₃AlO₅(OH)₄] followed by octahedral [Al(OH)2.5] and neutral [FeOOH] components, whereas in fine clays they are dominantly composed of tetrahedral component. These components have been defined in the model for soil amorphous ferri-aluminosilicates.