Unsupported iron Fischer-Tropsch synthesis catalyst, formed to a spherical shape and calcined in air, were carbided at 270°C with CO for 24 hours. Following carbiding, the material retained the shape and size of the calcined metal oxide. During agitation by rolling of a slurry, the average particle diameter decreased by about 50% during 450 hours; the attrited material retained a spherical shape so that size reduction was not due primarily to particle fracture. The average particle size (1/d3) was approximately linearly related to the rolling time, and the particle size distribution was fitted by the Weibull Probability Function.