Retorted and burnt shales prepared from rich and lean raw shales were blown through a 6-m vertical lift pipe and a small cyclone separator at gas velocities of 15 and 30 m/s, passing through the system either once or ten times. Size distributions of feeds and cyclone-bottom products were measured, as were those of some of the cyclone-top dusts. Aspect ratios of particles from the feedstocks and selected products were measured with the Quantimet 720. The size distributions of all the materials were downshifted during gasifying and cycloning, the lean, retorted shale only slightly, the rich, burnt material most severely. The new exterior surface area generated through attrition, estimated from the drag-mean particle size, rose as the square of the gas velocity and the 0.7 power of the number of passes. The aspect-ratio studies showed that the attritted particles were more rounded than the feeds and became more so with increasing gas velocity and repeated passes. This evidence, and the character of the size-distribution shifts, shows that the main mechanism of attrition of these materials is the breaking away and abrasion of asperities. Particle loading had no effect at all upon any of the size-distribution parameters or new-surface generation. This finding implies that attrition occurred by contact between particles and equipment walls rather than by interparticle collisions. It should therefore be less severe in larger equipment. 22 figures, 5 tables.