ATOMIC-FORCE MICROSCOPY STUDIES OF LAYER SILICATE MINERALS

The surfaces of silicate minerals are important in controlling a numbe r of geochemical phenomena from chemical weathering, to the transport of pollutants in solution. The atomic force microscope (AFM) has prove n invaluable for obtaining atomic resolution images of the surface top ology and structure of a wide variety of minerals. While the physical basis for the sample-tip interactions responsible for the images remai ns poorly understood, comparison of AFM images with the calculated bul k mineral structures, provides clear evidence that the AFM is truely c apable of resolving structural features on the atomic scale. The phyll osilicate or layered silicate minerals are particularly suited to stud y by atomic force microscopy because of their perfect {001} cleavage, wide range of structure types and variety of surface properties. Atomi c resolution images have been obtained on lizardite, chlorite, apophyl lite and muscovite. The AFM resolves the Angstrom-scale surface struct ure of these minerals and is able to clearly elucidate the different s tructural layers. These studies have been able to observe surface rela xation effects on the surface of chlorite, as well as the progressive amorphization (through ion beam damage) of the muscovite surface. Furt her, studies in solution are able to image the equilibrated near surfa ce structure providing fresh insight into the nature of the mineral-wa ter interface.