AMORPHOUS ALUMINUM HYDROXIDE FORMED AT THE EARLIEST WEATHERING STAGESOF K-FELDSPAR

Weathering products formed on the surface of K-feldspar in Yakushima I sland, Japan were investigated by X-ray powder diffraction (XRD), scan ning electron microscopy (SEM), transmission electron microscopy (TEM) , energy dispersive X-ray analysis (EDX) and X-ray photoelectron spect roscopy (XPS). XRD confirmed that the weathering products were compose d mainly of gibbsite and halloysite. SEM, TEM and EDX clearly showed f ormation of amorphous aluminum hydroxide exhibiting 2 distinct habits: 1) curled fibrous or circular forms less than 0.02 mu m in diameter; and 2) a spherical habit less than 1.0 mu m in diameter The fibrous al uminum hydroxide exhibited curled fibrous forms or circular forms less than 0.02 mu m in diameter and gave a diffuse electron diffraction ha lo. EDX indicated that the material consisted mainly of Al and very sm all amounts of Si and Fe. The spherical aluminum hydroxide also gave s imilar EDX and electron diffraction characteristics to the fibrous mat erial. These fibrous and spherical aluminum hydroxides must be formed as a metastable phase in the earliest weathering stages, and transform ed into a stable phase of gibbsite and halloysite as the reaction proc eeded.