A systematic study, focusing on the characterization of inelastic deformation and the transition from elastic to inelastic deformation in two transparent fine-grained polycrystalline spinels (MgAl(2)O(4)) with different grain sizes, has been conducted using depth-sensing indentation techniques at high loads. Congruent experiments included observations on the evolution of indentation damage, examinations of the sub-surface damage zone and inspection of the remnant surface profiles of the impressions. Indentation stress-strain behavior obtained from analysis of load-displacement curves revealed a small difference in yielding and strain-hardening behavior even though there was a significant grain size difference. Directly below the indentation sites, regions of grain boundary cracking, associated with the inelastic zone, were identified in both spinels. Comparison of the Meyer hardness and in-situ hardness showed a discrepancy at low loads, which is a result of elastic recovery. It is proposed that spherical indentation could serve as a useful method of evaluating armor materials, particularly when the behavior is described using indentation stress and strain for the onset and development of inelastic deformation under high contact pressures and self-confining stresses.