The symmetric Laue diffraction of Mössbauer rays is analyzed in the spherical-wave approximation. The saddle-point method is applied to calculate the-photon wave function within the Borrmann triangle in a thick crystal with strong nuclear absorption. Both the Rayleigh and resonant nuclear scatterings are taken into account. The interference oscillations of the diffracted beam intensity are shown to appear in the case of the Rayleigh scattering of Mössbauer radiation, which may be used for precision measurements of crystal parameters.