Acid mine drainage refers to the acidic outflow of water from a mining site caused by the weathering of pyrite, FeS₂, which is present in coal. Oxidation of pyrite, within underground mine work and surface waste, releases sulfuric acid and metals, such as nickel, cobalt, arsenic, and lead into surface and subsurface waters. AMD negatively impacts water quality, wildlife, and human health. The aim of this study was to determine changes in pyrite particle size, morphology, texture, and composition during the weathering of the parent coal-shale rock. This was accomplished by collecting scanning electron microscopy (SEM) images and energy dispersive spectroscopy (EDS) element maps of pyrite in the following materials: (1) the parent coal-shale rock; (2) rock powder before and after simulated weathering; and (3) soils developing on historic mine waste. Shale samples were crushed to 63, 250, and 2000 µm and subjected to an artificial weathering process over several months to observe if particle size impacted the degree of weathering and its effect on mineral morphology. Soils were collected at various depths and prepared as thin sections. The commonest morphologies and textures seen were framboidal, octahedral, porous, oxidation rims, and replacement textures. Oxidation rim textures are most abundant in the soils. Iron and sulfur oxide concentrations observed over a range of particle sizes (1 µm to 2000 µm) and surface topographies (uniform to highly variable) indicate that oxidation increases as particle size decreases. Preliminary results suggest the release of AMD worsens as topography and particle surface area increase.