Log analysts have recently become reacquainted with the fact that formation resistivity is actually a complex quantity. It has a reactive as well as a resistive component, both of which vary with frequency. The phenomenon has been known and exploited in metal mining exploration for many years. It is commonly referred to as "induced polarization" or IP and more recently as "complex resistivity". The reactive component of the complex formation resistivity is affected by the rocks’ cation exchange capacity as well as by the presence of disseminate metallic conductors. Thus, measurements of complex formation resistivity bears importantly on the estimation of shaliness.