Microfine rock aggregates, formed naturally or in a crushing process, pass a #200 ASTM sieve, so have at least two orthogonal principal dimensions less than 75 mu m, the sieve opening size. In this paper, for the first time, we capture true 3-D shape and size data of several different types of microfine aggregates, using X-ray microcomputed tomography (mu CT) with a voxel size of 2 mu m. This information is used to generate shape analyses of various kinds. Particle size distributions are also generated from the mu CT data and quantitatively compared to the results of laser diffraction, which is the leading method for measuring particle size distributions of sub-millimeter size particles. By taking into account the actual particle shape, the differences between mu CT and laser diffraction can be qualitatively explained. (C) 2007 Elsevier B.V. All rights reserved.