The Effects of Abrasion on the Size, Shape and Roundness of Rock Fragments

Earlier work on the abrasion of rock fragments in tumbling barrels is reviewed, and the main principles are summarized. Most earlier work concerned one or another aspect of abrasion without including interrelations among particle characteristics during wear. Experimental data are presented on size, sphericity, and roundness during abrasion, and the relative rates of size reduction, rounding, and shape change are determined. It is found that the coefficient of rounding is largest, the coefficient of shape change is intermediate, and the coefficient of size reduction is smallest. An analytical theory of abrasion is developed on the basis of the experimental data, and it is found that simple exponential functions yield at least first approximations to the size and shape aspects of particle wear. Rounding is a more complex process, controlled in part by the shapes of the particles. Geological applications of tumbling-barrel data are discussed, and it is emphasized that wear of rock fragments is only one aspect of the changes which sediments undergo during transportation. The selective effects of transportation, in terms of size, shape, and density, must be taken into account in any analysis of actual field relations.