Etch-Pit Measurements on Scanning Electron Micrographs of Weathered Grain Surfaces

Digital image analysis (DIA) was successfully used to evaluate the size and shape distribution of etch pits on the surfaces of weathered hornblende and microcline grains. An interpretative tracing of the image of etch pits and grain perimeter from projected SEM micrographs was used. Histograms of size-frequency distributions of etch pits proved useful for comparisons between grains, while plots of shape factors of etch pits allowed an evaluation for individual grains. Manual calculation of etch-pit density with a dot grid overlay gave results similar to those with DIA, although with less variation on replication. Precision with both methods was associated with operator interpretation of the grain surface, and consistency in interpretation.