Abrasion of sedimentary particles in fluvial and eolian environments is widely associated
with collisions encountered by the particle. Although the physics of abrasion is complex,
purely geometric models recover the course of mass and shape evolution of individual
particles in low- and middle-energy environments (in the absence of fragmentation)
remarkably well. In this paper, we introduce the first model for the collision-driven
collective mass evolution of sedimentary particles. The model utilizes results of
the individual, geometric abrasion theory as a collision kernel; following techniques
adopted in the statistical theory of coagulation and fragmentation, the corresponding
Fokker–Planck equation is derived. Our model uncovers a startling fundamental feature
of collective particle size dynamics: collisional abrasion may, depending on the energy
level, either focus size distributions, thus enhancing the effects of size-selective
transport, or it may act in the opposite direction by dispersing the distribution.