Title: Desilication of Halloysite and Its Relation to Gibbsite Formation
Abstract: The evidence presented points to the alteration of halloysite to gibbsite. Mineralogical data, as determined by X-ray and differential analysis, verify identification of halloysite and gibbsite. Chemical data confirm the expected lower silica and higher alumina content for samples which are predominantly gibbsitic. It is reasonable to assume from petrographic evidence that gibbsite develops by desilicarion of halloysite. Halloysite amygdules undergo desilication along the outer peripheries, where acid silica-deficient waters pass, attacking the halloysite by dissolving silica. Halloysite is stable only if it is protected from such solutions , or if the solution passing by is saturated with silica. Whereas alteration of feldspar to halloysite involves a gain in volume, a loss in volume follows desilication of halloysite. This loss in volume is exemplified by the surface cracks clearly visible in the desilicated halloysite. IN AN EARLIER PAPER Sherman and Ikawa (1959) described the occurrence of gibbsite amygdules in the Haiku bauxite area of Maui, Hawaii. At that time it was proposed that gibbsite amygdules formed in rock vesicles by rhythmic precipitation of hydrated alumina. Subsequent and more thorough investigation of the same area and elsewhere in the Hawaiian Islands suggests a more complex sequence of events in the development of these gibbsite amygdules. In this paper the results of field and laboratory studies are presented to explain halloysite formation and its subsequent desilicarion to gibbsite. Bates (1962 ) suggested that gibbsite is produced in Hawaii by (1) removal of silica from halloysite, (2 ) dehydration of aluminum gel, and ( 3) precipitation from solution. The first mode of formati on is of primary interest in this study.
Publication Year: 1966
Publication Date: 1966-01-01
Language: en
Type: article
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Cited By Count: 5
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