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It has been found that factional frequency 1/f noise in crystal oscillators is generated by the energy dissipated in the resonator. Earlier investigations found the same origin of 1/f noise also in quartz resonators. In the present contribution we shall show that the losses connected with the current flow through the resonator generate frequency fluctuations which are changed into 1/f phase fluctuations due to the transportation delay. Further we shall prove that the magnitude of the corresponding Power Spectral Density (PSD) is independent of the resonator resonance frequency, fo, since it is function of the material constant Qfo. In addition, we will present a theoretical PSD model of the phase noise at the output of the resonator with a discussion on the 1/f2 and 1/f3 slopes. Finally, we shall investigate contribution of the white noise on the measurement and shall discuss the Allan variance for the resonator and an eventual crystal oscillator.