Mechanical behavior of synthetic omphacite aggregates at high temperature and high pressure Triaxial compression experiments were performed on the synthesized samples and Fe bearing clinopyroxenite in a solid medium apparatus at a confining pressure of 0.75 to 2.5 GPa temperatures 900 to 1175oC and strain rates between 1.1x10 6 s 1 to 8.5x 10 5 s 1. Samples of calcic compositions deformed at high differential stresses reveal abundant mechanical (100)[001] twins whereas jadeite aggregates deformed at low differential stress show well developed subgrain boundaries. Combining the mechanical data and observed microstructures for deformed synthetic samples reveal that the deformation of diopside aggregates is controlled by dislocation glide while the kinetics of dislocation climb controls the deformation of jadeite aggregates. The variation in strength with composition obeys scaling by the dependence of melting temperature and shear modulus on composition. In contrast to climb controlled deformation glide controlled deformation should be insensitive to impurity concentrations.