Illite is a layered, aluminosilicate clay mineral in which K+ dominates the interlayer spaces. The frayed edges of the interlayers provide high affinity sites for 137Cs+ in contaminated soils as well as important plant nutrients (K+ and NH4+). We know that oxalate, a common plant root exudate, accelerates Cs release from illite. Large mica particles are degraded from the outer edges inward from reactions with organic acids. It is not known, however, if the structurally similar, but colloidal illite particles, weather in the same way. We are seeking to determine if atomic force microscopy (AFM) can be used to quickly and accurately quantify the physical changes at the nanometer scale and elucidate weathering mechanisms. In this study, we have developed consistent dispersion methods that allow us to observe individual illite particles by AFM. By comparing the particle thickness distributions determined by AFM with those by x-ray diffraction, we determine the most effective and reproducible dispersion techniques. We can also determine the extent of particle weathering as a result of oxalate treatment.