Immersion of Ti3SiC2 samples in molten cryolite at 960 degrees C resulted in the preferential diffusion of Si atoms out of the basal planes to form a partially ordered, cubic phase with approximate chemistry Ti(C-0.67, Si-0.06) The latter forms in domains, wherein the (111) planes are related by mirror planes; ie., the loss of Si results in the de-twinning of the Ti3C2 layers. Raman spectroscopy, X-ray diffraction, optical, scanning and transmission electron microscopy all indicate that the Si exits the structure topotactically, in such a way that the C atoms remain partially in their ordered position in the cubic phase.