The exergy assessment of the mineral capital on Earth has been usually calculated as the minimum and actual exergy required for replacing the minerals in composition, concentration and quantity from a completely degraded state where all resources have been extracted and dispersed to the conditions found currently in Nature, i.e. from what we call Thanatia or the Crepuscular Planet to the mine conditions. In this evaluation, we have assumed that the concentration exergy is calculated as the minimum energy involved in concentrating a substance from an ideal mixture of two components, which is only strictly valid for ideal mixtures. When there is not chemical cohesion among the substances, it remains valid for solid mixtures. But the cohesion energy is always present in any mineral. Hence, the aim of this paper is twofold: 1) it explain show to calculate the comminution exergy for any mineral or rock as a function of the comminuted size, and 2) what should be the reference level for the average size fragment in the Crepuscular Planet. The results of the study indicate that the comminution exergy term is very low compared to the concentration exergy and can be neglected when assessing the exergy of naturally comminuted minerals found in mines having Thanatia as reference. Nevertheless, as industry requires in most of cases very fine grain sizes, industrial comminution consumes very large amounts of exergy and cannot be neglected. (C) 2012 Elsevier Ltd. All rights reserved.