Allophane isolated from a podsol developed on a non-vitric parent material

Abstract

The relationship between allophane, an X-ray amorphous, short-range ordered aluminosilicate gel, found in soils derived from volcanic ash (Andosols) and the poorly ordered clay minerals present in the subsoils of podsols (Spodosols) developed on non-vitric parent materials is uncertain. The similarity of many of the physical and chemical properties of these soils has led to postulations that ‘allophane-like’ materials also occur in podsols^1–4. The high chemical reactivity of allophane and its intimate association with both soil organic matter and crystalline phyllosilicates and oxides has meant that earlier studies have involved either the examination of mixed crystal-line–microcrystalline clay systems, or the use of dispersing reagents that would have caused at least the partial solution of any poorly ordered phases present. The established instrumental techniques of differential thermal analysis and IR absorption spectroscopy may be used to characterise allophanic materials, but only when they constitute virtually the whole of the clay fraction⁵. The present study characterises an allophane sample successfully isolated from a podsol profile.