ABSTRACTExperiments were performed using a tumbling’mill containing gravel-sized ceramic spheres and crushed Brazilian quartz sand to simulate comminution in high energy, mixed sediment fluvial environments. Results show that the sand is quickly reduced to silt (16 hours at 155 rpm) by a sequence of edge chipping, partial cracking, splitting and crushing. Comminution is most rapid at higher rotation speeds but significantly occurs even at the lowest speed of 55 rpm. Approximately 50% of the angular silt produced lies in the size range 20–63μm characteristic of loess-sized silt. Under suitable conditions‘fluvial crushing’could provide a viable mechanism for some silt production in high energy environments such as meltwater streams and the turbulent bores of flash floods.