Morphology of Allophane, Imogolite and Halloysite

Abstract

Volcanic ash soils were studied with the scanning electron microscope to observe the morphology and occurrence of aUophane, 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.

Characterization, functioning and classification of two volcanic soil profiles under different land uses in Central Mexico

“…5). Halloysite in volcanic ash soils can result from the direct weathering of feldspars (Eswaran, 1972;Chartres and van Reuler, 1985) or from the re-silication of allophane (Wada, 1989). The XRD of the forest profile shows the same primary minerals than those observed in the maize profile.…”

Physico-Chemical Properties of Imogolite Nanotubes Functionalized on Both External and Internal Surfaces

“…Its structure consists of a single continuous gibbsite Al(OH) 3 sheet, in which, on one side only, three OH groups are substituted by an orthosilicate unit O 3 SiOH. Si–O bonds are shorter than Al–O bonds, so the gibbsite-like sheet curls up, forming nanotubes with an inner surface lined by silanols and an outer surface covered by bridged Al(OH)Al species (Scheme ) …”

Scanning Electron Microscopic Study of Imogolite Formation from Plagioclase

“…Imogolite is a fibrous clay mineral that occurs in young, glassy volcanic ash soils (Yoshinaga, 1970;Yoshinaga et al, 1968, Wada andMatsubara, 1968;Wada et al, 1970Wada et al, , 1972Honda, 1972;Tazaki, 1971Tazaki, , 1975Eswaran, 1972;Noishiki and Tazaki, 1975). Although it has previously been shown to form by the alteration of volcanic glass, the present study describes the formation of imogolite from plagioclase grains in volcanic ash.…”