The surface chemistry of naturally weathered hornblende has been analyzed using Auger Electron Spectroscopy. The high spatial resolution and depth profiling capabilities of this technique allow changes in the relative concentrations of cations to be determined over micron-scale areas and at depths resolvable on the sub-micron scale. These data indicate that during chemical weathering: 1) there is a systematic change in surface chemistry through a thickness up to 1200 angstroms, 2) complete cation depletion at the surface layer does not occur, 3) different components are leached to different depths to varying degrees, and 4) no new phase such as clay or smectite necessarily forms. A nonsteady state diffusion model is most consistent with these data.
