There are many applications in the mining industry where various material features may only be calculated by means of an image analysis method. Good examples of this are size analysis of open-pit muckpiles, on-line size analysis of ore on a belt conveyor, mineralogical composition analysis by microscopy, lithological composition of an ore, and on-line analysis of flotation froth etc. In all cases the analysis is performed on a two-dimensional basis whereas the information is required on a three-dimensional (volumetric or weight) basis. In most cases, an area particle distribution is first obtained, and then a complex stereological transformation is used to obtain the required weight particle distribution. In this paper a simpler approach is presented. The procedure was developed from the well-known equation for calculating weight distribution from measured surface distribution, adapting the Heywood equations on shape factors, and establishing a thickness model. The new procedure has been experimentally tested using samples from seven different lithologies present in Andina, copper ore. Good results have been obtained for estimating granulometric distributions and lithological compositions. It is concluded that this procedure constitutes a simpler, yet satisfactory approach. (C) 2003 Elsevier Science Ltd. All rights reserved.