In our previous study, the effects of added kaolinite on the microstructure and strength of freeze-cast composites of kaolinite platelets and silica nanoparticles were reported. This current article details the results of an investigation into the effects of the kaolinite on the microstructure and phase transformation of these materials during sintering. It is found that upon sintering at 1000 degrees C, grain growth and phase transformation of the silica nanoparticles in the silica/kaolinite composites are hindered, and even completely inhibited, at sufficient concentrations of added kaolinite. Nonetheless, reduction in the size of the nanoparticles suggests that diffusion from silica nanoparticles to kaolinite platelets is occurring. Upon increasing the sintering temperature to 1250 degrees C, boundaries between the two species completely disappear and new peaks are observed in the X-ray diffraction pattern of the composite that are not present in the patterns of either silica-only or kaolinite-only samples. These findings indicate that a transitioning interfacial phase forms at higher temperatures.