Relation of certain geometrical features to the dielectric anomaly of rocks

We show that the real part of the dielectric constant e′ of rocks at low frequencies can be anomalously high due to the presence of a small concentration η of high aspect ratio particles. For oblate spheroidal grains (a≪b=c) with depolarization factor along symmetry (-a) axis, Ls≅1-δ, δ=πa/2b, the static value of the dielectric constant of rock es and dc conductivity σ(0) are given for (1)δ ηbyσ(0)≅σR(1-η/δ), es≅ηe′m/δ2. Here e′m is the dielectric constant of the grain; σR is the dc conductivity of the host rock. Case (1) corresponds to the well known Maxwell‐Wagner effect with es diverging as η → 0, and σ(0)→0. Case (2) gives a novel result that es may diverge for δ>η≫δ2, with a nonvanishing σ(0). Case (2) is applied to explain frequency and salinity dependences and the giant values (∼104) of the dielectric constant of conducting sedimentary rocks. For η∼10-4, δ∼10-3, e′m=10, we find es∼1000, which is large compared to e′m or the dielectric constant of water e′w(∼80).