A boundary [[acoustic]] wave as a liquid-solid interface (i.e., [[formation]] wall at the borehole) resulting from the interaction of the [[compression wave|compressional wave]] in the liquid and the shear wave in the solid. By definition, the Stoneley wave must have a [[wavelength]] smaller than the borehole diameter. Particle motion in the solid wall will be elliptical and retrograde similar to a [[Rayleigh wave]]. The velocity of the Stoneley wave will be less than that of the compressional wave in fluid or the shear wave in the solid. See also [[tube wave]].