The mechanical behavior of the cubic spinel SiAlON polymorph (c-Si 6Àz Al z O z N 8Àz , z = 1), was modeled using an ab initio den-sity functional technique. The cubic spinel structure exhibits a maximum stress response of $33 and $40 GPa, for the applied c 11 and c 23 components of strain, respectively. An existing empirical technique was employed to determine the hardness of the SiAlON crystal: $40 GPa. For completeness the hypothesis of the empirical formalism is discussed.