The results of experimental and theoretical studies of low-frequency effects of amplitude dependent internal friction (nonlinear losses and resonance frequency shift) and generation of second and third harmonics in an acoustic bar resonator made of Karelian granite are presented. The analytical description of the observed effects is performed within the framework of phenomenological hysteretic equations of state containing elastic and inelastic hysteresis. It was shown that elastic cubic hysteresis is manifested at small amplitudes of strains, whereas superposition of elastic and inelastic quadratic hysteresises occurs at large amplitudes of strain. Relative weights of these hysteresises and effective parameters of acoustic nonlinearity of granite are determined.