Bentonite-derived monolithic materials with and without distributed nanoscale turbostratic carbon, obtained by hot-pressing organobentonite and bentonite particles, respectively, in the absence of an added binder, exhibit exceptionally high dielectric loss while the electrical conductivity is relatively low. The combination of high dielectric loss and relatively low conductivity has not been previously achieved. An additional advantage of these materials is their high-temperature ability. An application relates to electromagnetic absorption in electronic warfare. Both materials comprise mullite, cristobalite, and disordered clay. The organobentonite-derived material also contains carbon due to organic pyrolysis and exhibits loss angle delta 84.04A degrees-89.52A degrees, the real part of the relative dielectric constant 7.2-25 and conductivity 7.7 x 10(-5) to 1.7 x 10(-8) S/cm over the frequency range from 10 Hz to 2 MHz (relevant to military communication with submarines and to beacons for aircraft and marine navigation); with increasing frequency, delta decreases, the real and imaginary parts of the relative dielectric constant decrease, and the conductivity increases, all without peaks in the frequency dependence. For the material derived from bentonite, delta is high only above 1400 Hz. The carbon reduces the dielectric connectivity but enhances the conduction connectivity, with the effects decreasing with increasing frequency; it causes the real part of the relative dielectric constant to decrease below 200 Hz, and the absolute value of the imaginary part, conductivity, and delta to increase below similar to 1600 Hz and decrease above similar to 1600 Hz.