Abstract: Experimental alteration of albite in deionized-distilled water at 150° to 225°C for various times up to 30 days was performed to elucidate formation processes for alteration products of albite in aqueous solution. The alteration products were examined by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy (TEM), and energy dispersive X-ray analysis (EDX). The surface compositions of albite before and after alteration were investigated by X-ray photoelectron spectroscopy (XPS). TEM clearly showed that an amorphous leached layer was produced on the albite surface at the earliest alteration stage together with small amounts of allophane. The leached layer increased successively in thickness and tended to be detached from the albite surface as alteration proceeded. Noncrystalline fibers less than 0.5 µm in length appeared within the leached layer matrix and transformed into thin flaky smectite and small amounts of K-mica. The leached layer gave electron diffraction patterns with a diffuse halo, whereas the flaky smectite displayed rings at 4.51, 2.61, and 1.54 Å. EDX confirmed that the flaky smectite consisted mainly of Si and Al, and small amounts of Na. The smectite was formed in the stability field of Na-smectite for the system of Na2O-Al2O3-SiO2-H2O.