Utilizing the method of optical diffraction produced by acousto-optical interac-tion, we have studied both surface and bulk acoustic waves from the optical diffraction patterns or the inverse phase velocity surfaces excited by interdigital transducers in quartz, with special emphasis on these waves produced in the z-cut crystal. A SAW different from normal Rayleigh waves has been found. On the ground of a brief discussion, we conclude that in many aspects the nature of this wave and/or similar wave disturbances is worthy for further investigations.