The alteration of diabase dikes at King Mountain, Kiowa County, Oklahoma, illustrates the diversity of clay mineral alteration products which may result from very local variations in the "micro-environment." Three diabase dikes exhibiting varying degrees of argillation are exposed in a one-hundred-foot-deep railroad cut. The diabase and its alteration products were examined by means of the petrographic microscope, X-ray diffraction aim electron microscopy. Chemical characterizations were obtained by means of chemical analysis by X-ray fluorescence differential thermal analysis and effluent gas analysis. Diabase from the center of the railroad cut contains 52% labradorite (An 59) and 31% chlorite. The chlorite is interpreted as a deuteric alteration product of the original pyroxene. As a weathering surface is approached at the east end of the railroad cut, the relatively fresh labradorite, chlorite and magnetite are replaced by goethite, interstratified illite-montmorillonite and kaolin. The oxidization and leaching has been accomplished by the downward percolation of groundwater along a steeply dipping dike. The same diabase dike contains interstratified chlorite-montmorillonite where relief is low and alkaline conditions persist. Tile clay mineralogy, clay mineral distribution and chemical data all support a weathering origin for the argillation. The clay mineral diversity has resulted from very local. relief-controlled variations in the chemical environment.