Abstract: Volcanic ash soils were studied with the scanning electron microscope to observe the morphology and occurrence of allophane, imogolite and halloysite. Allophane and imogolite in general were randomly distributed indicating a process of dissolution and recrystallization. Halloysite is typically associated with feldspars showing that it is formed by direct alteration.
The imogolite fibres studied with the SEM show them to be much thicker than currently reported in the literature and it is thought that pretreatment of the clays for TEM measurements results in a partial destruction. Halloysite consists typically of short rigid tubes and thus differs from imogolite which tends to curl.