Endogenous growth theories have paid insufficient attention to patterns of growth within subgroups of developing countries. Partly drawing on these theories, a mixed endogenous growth-technology diffusion model is formulated with regard to developing mineral economies, The model envisages an S-shaped double convergence long-term equilibrium, with the flex point possibly lying above the corresponding point for non-mineral economies, The performance of a mineral economy is assumed to depend, among other factors, on the growth and instability of its main mineral commodity export price. The model is tested on cross-country data.