Induced polarization (I P) occurs at metal-solution and membrane-solution interfaces in rock materials. Minerals producing significant I P include sulfides, magnetite (electrode polarization), and some clays (membrane polarization). In mineral exploration, one is concerned with the distinction between these 2 phenomena; either may be significant, but together they are confusing. While no practical means has yet been devised to do this in the field, one may exist. The present study represents the first stage in an attempt to elucidate the phenomena and to make such a distinction. There is no means of studying directly the effect of variables on polarization at a single interface or cell in a rock if those variables also affect rock resistivity. Hence, one must speak of rock I P independently of individual cell I P. Data reported herein reflect rock I P. Temperature and pressure appear to have little effect on I P of specimens studied so far; further investigation may show that they are important in some geologic environments. Changes in electrolyte activity greatly influence rock I P. Membrane and disseminated electrode polarization decrease while connected (veined) electrode I P increases with increasing activity. This fact may be useful in interpretation of depth variations of I P in the field, particularly over oxidizing sulfide bodies.