Complex permittivity of common minerals and one soil at low water contents

The complex permittivity of quartz, feldspars, calcite, and non-crystalline gypsum at 4%-7% volumetric water content shows low conductivity and low-frequency dispersion. At similar water contents, montmorillonite, gypsum crystallites, and a desert soil all show unusually strong and broad low-frequency dispersion, and strong attenuation rates above 100 MHz. The desert soil contained 80% quartz, 10% feldspars, and 10% gypsum, with the gypsum appearing as crystallites and crustations on the quartz particles. Despite insignificant salt or clay mineral content, the dispersion and attenuation rates of the soil exceed those of its constituents and are similar to that of montmorillonite, with a rate exceeding 100 dB m^-1 by 1 GHz. We attribute this to a Maxwell-Wagner type of relaxation, likely caused by polarization resulting from surface charge and from the charge separation caused by dielectric and conductivity contrasts between the gypsum and quartz. The conductivity contrasts were likely enhanced by ions dissolved from the gypsum and feldspars into free water within, and water adsorbed on the quartz surfaces.