An analog circuit digital computer setup was used to evaluate rock electrical impedance and phase angle in the frequency range 0.05 to 2 khz. Room-temperature measurements were made on several samples of basalt, granite, and quartz. Argand diagram presentation of rock reactance as a function of its resistance at a series of frequencies described a semicircular arc. Rock impedance circular arcs can be used to define the rock resistivity at infinite frequency and the dc resistivity at the limit of zero frequency. Variation of rock resistance with the logarithm of frequency indicated finite rock dielectric dispersions at characteristic frequency ranges. Also, variation of rock reactance with the logarithm of frequency exhibited finite relaxation peaks, which can be used to define the rock characteristics or turnover frequency as well as a characteristic or relaxation time.