Abstract We have measured the dielectric anisotropy of specimens of a slate that formed by a single episode of metamorphism and deformation of a volcanic tuff. The dielectric anisotropies can be represented by oblate ellipsoids that are comparable in shape with the strain ellipsoids determined from the changes in thickness of the rims of accretionary lapilli in the slate. The rocks studied are largely made up of platy chlorite grains, and discs cut parallel to the schistosity often exhibit an anomalous low-frequency dispersion. The magnetic susceptibility anisotropies are also oblate but their shapes do not compare as well with the strain as they have less extreme ellipsoidal shapes.