The size distribution of the diamonds in a kimberlitic rock is a negative exponential function-i.e., the frequency of large diamonds diminishes exponentially with increasing size. The number of microdiamonds in narrow fine sizes allows predicting the probability of discovering coarser valuable diamonds. For deposit evaluation, the microdiamonds are recovered in the solid residue of the leaching of some hundreds kilograms of rock samples. Computed tomography (CT) systems-based on nano- and micro-focus X-ray sources and high-resolution detectors-capable of scanning drill-hole cores have been indicated as a possible practicable alternative to leaching for microdiamond studies. A simple model is developed that allows valuating the size of the microdiamond detectable with a given X-ray tube spot size and detector Modulation Transfer Function (MTF). Basically, the model describes the diamond as a nodule of known attenuation, projects it on the detector plane with a given magnification, resamples the magnified nodule according to the detector pixel array, calculates the frequency content of the nodule on the detector plane by FFT, composes the frequency content with the overall MTF of the system and by FFT-1 recalculates the object. By comparing the reconstructed object with the original one, the lost in attenuation and the blurring due to the radiography system can be evaluated. Preliminary experimental tests with synchrotron radiation were carried out to characterize the X-ray attenuation properties of the kimberlite and evaluate the resolution in relation to the mineral texture. Both commercial X-ray micro-CT systems and a number of different systems assembled in our laboratories combining different components were tested and compared with a phantom core. (C) 2004 Elsevier B.V. All rights reserved.