Surface phase transition of hydrated calcium oxalate crystal in the presence of normal and stone-formers' urine.

Crystals of calcium oxalate monohydrate (COM), dihydrate (COD) and trihydrate (COT) were grown by slow diffusion of reacting ions from solutions using interfacially controlled crystallization. Phase transition of COT to COD and COM, and COD to COM were studied on single crystal by X-ray diffraction analysis of the same crystal before and after exposure to normal and stone formers' urine. Phase transition on the surface of single crystals has been demonstrated by SEM energy dispersive X-ray microanalysis using windowless detector, and scanning Auger electron microprobe. Data obtained in this study offer direct experimental evidence for phase transformation on the surface of the hydrated calcium oxalate single crystal. In presence of normal urine the surface of COT single crystal undergoes transformation into COD and in presence of recurrent calcium oxalate stone former's urine surface transformation to COM takes place.