The shear mechanism in the clinoenstatite (space group C2/c)-akimotoite (space group R3) transition under high-pressure can be explained by a sweeping of partial dislocations associated with cooperative cation displacements without any long-range atomic diffusion. The shortest translation vector, [001] on the (100) plane of clinoenstatite, dissociates into a 1/3[001] + 1/6[011] + 1/3[001] + 1/6[011] vector, and the first two partial dislocations bring about a hexagonal close packed oxygen sublattice in the akimotoite structure. This shear mechanism is considered to be a favorable mechanism under high differential stress, or at high-pressures and relatively low-temperatures, where any overpressure from the hypothetical equilibrium clinoenstatite-akimotoite phase boundary would be high, but atomic diffusion would be kinetically hindered. Therefore, this mechanism would occur in subducting cold slabs in the Earth's deep mantle and in shocked meteorites.