ANALYTICAL TRANSMISSION ELECTRON-MICROSCOPE STUDIES OF PLAGIOCLASE, MUSCOVITE, AND K-FELDSPAR WEATHERING

Suggests a sequential formation of weathering products. An alteration layer <1 μm thick on feldspar surfaces had short-range order and was termed protocrystalline. Recrystallization of the patchily developed protocrystalline rind produced Fe-bearing, aluminous smectite, which was ultimately replaced by spherical halloysite and laths of kaolinite. Kaolinite was the stable weathering product of the feldspars and muscovite in the profiles. It probably formed in equilibrium with a solution whose composition was no longer controlled by the microenvironment within the feldspar, but approached that of meteoric water. -from Authors