Formation of imogolite and allophane in shattered sandstone underlying brown forest soil

Abstract

The occurrence of imogolite, as gel films associated with allophane, in the fractures of shattered sandstone is being reported. The sandstone was overlain by a Brown Forest soil about 50 cm thick, derived from the same sandstone, in which neither of the minerals was found to be formed. The mode of occurrence of the minerals was similar to that in a fresh gravel bed (Iapilli-fall deposit) underlying an ash-derived soil and in podzols from many locations. This, together with the results of a synthetic experiment with soil solutions extracted, suggested that imogolite and allophane in the shattered sandstone were formed by precipitation of a hydroxy-Al orthosilicate complex transported from the overlying soil horizons. The finding suggests that imogolite and allophane may be distributed in soils more widely than hitherto reported, irrespective of the type of parent materials and type of soils.