All C ij values are positive. Their combinations obeying the rules pertaining to the mechanical stability of the phase, and the equations providing bulk B V and shear G V moduli are as follows for the tetragonal system: and G V moduli are somewhat larger than those of 'glitter', but still smaller than moduli accepted for diamond i.e. B V =445 GPa and G V = 530 GPa (cf. and references therein).