Compacted pellets composed of alternate layers of KCl and PbCl2, separated by discontinuous layers of graphite flakes, were fired at 350 to 370 °C for 7 to 10 days at both atmospheric pressure and 70 bar. Aggregates of K2PbCl4 and KPb2Cl5, resembling porphyroblasts in appearance, formed at reactant interfaces. Formation of these aggregates was accompanied by mechanical displacement of graphite. Volume calculations indicate that displacement of graphite occurred because of simultaneous volume loss and gain on opposite sides of the oiriginal interface. A “crystallization force” was not necessary for the displacement. It is suggested that a similar mechanism of chemical rearrangement should be considered a viable possibility for matrix displacement during porphyroblast growth.