A simple procedure is developed for simulating elastic compositions of substances as may occur in exogeologic bodies. It is based on a mixing law using acoustic slownesses obtained by averaging elasticities of crystallite aggregate components. The method applies to materials having an arbitrary number of constituents; illustrative examples are given for two-component solid solutions in the olivine and pyroxene families. The averaging algorithm is also applied to perovskite, post-perovskite, and alumina elasticities. Linear temperature and pressure coefficients are estimated for the perovskites; higher-order temperature coefficients are computed for alumina. Debye temperatures are given for the various simulants.