The phase transformation of graphitelike BN (h-BN) to wurtzite-type high-pressure BN (w-BN) was investigated through shock-recovery techniques under quasihydrodynamic and nonhydrodynamic shock compressions and under various strain conditions. The experimental results support a diffusionless mechanism, by which the hydrodynamicc-axis compression ofh-BN is preferred. This mechanism is topologically considered based on the relationship of crystal structures betweenh-BN andw-BN. The presence of deviatoric stress and strain depresses the yield ofw-BN and the development ofw-BN (100) relative to (002). ©1997 American Institute of Physics.