Solid-particle erosion studies were conducted on geopolymers derived from various combinations of granulated blast-furnace slag, flyash, sand, clay, and rock. The erodent particles were 390-mu m angular Al2O3, which impacted at 30, 60, or 90 degrees at a velocity of 50, 70, or 100 m/s. Steady-state erosion rates were obtained as weight of target lost per weight of impacting particles. Material-loss mechanisms were studied by scanning electron microscopy (SEM). All of the geopolymers responded to normal impact as conventional brittle solids, but impact at 30 degrees led to anomalously rapid erosion, probably because of presence of microcracks and consequent enhanced removal of aggregates within the geopolymers. Erosion rates at 90 degrees impact were proportional to erodent velocity to the 2.3-2.7 power. The geopolymers exhibited crushing strengths of approximately 32-57 MPa. Erosion rate correlated with density and strength for geopolymers of similar composition. All of the geopolymers that contained flyash were more resistant to erosion than was the geopolymer without flyash.