The clinopyroxenes kanoite and spodumene were studied by single-crystal X-r
ay diffraction in a diamond anvil cell (DAC) at room temperature. At the di
splacive phase transitions between the C2/c and P2(1)/c polymorphs both pha
ses coexist within the same crystal. In this two-phase region the pressure
in the DAC remains constant. The experimental results demonstrate that pres
sure buffering at first-order phase transitions call occur in the DAC.