Desilication of Halloysite and Its Relation to Gibbsite Formation

摘要

The evidence presented points to the alteration of halloysite to gibbsite.Mineralogical data, as determined by X-ray and differential analysis, verifyidentification of halloysite and gibbsite. Chemical data confirm the expected lowersilica and higher alumina content for samples which are predominantly gibbsitic. Itis reasonable to assume from petrographic evidence that gibbsite develops by desilicarionof halloysite. Halloysite amygdules undergo desilication along the outer peripheries,where acid silica-deficient waters pass, attacking the halloysite by dissolvingsilica. Halloysite is stable only if it is protected from such solutions, or if the solutionpassing by is saturated with silica.Whereas alteration of feldspar to halloysite involves a gain in volume, a loss involume follows desilication of halloysite. This loss in volume is exemplified by thesurface cracks clearly visible in the desilicated halloysite.