Diffraction of synchrotron radiation in crystals of potassium chromate and germanium reveals a tetrahedral anisotropy of anomalous (resonant) scattering with respect to polarization and wave vectors that introduces a third-rank tensor into the intensity equations. This tensor arises from a mixed dipole-quadrupole term that vanishes for forward scattering and for centrosymmetric atoms. At resonances 13 eV below the Cr K edge and 7 eV above the Ge K edge large changes of intensities with rotation of azimuth are observed for weak and forbidden Bragg reflections in agreement with the optical model.