Microwave dielectric properties of dry rocks

The use of a combination of several measurement techniques to investigate the dielectric properties of 80 rock samples in the microwave region is discussed. The real part of the relative dielectric constant ε\´ was measured in 0.1-GHz steps from 0.5 to 18 GHz, and the imaginary part ε" was measured at five frequencies extending between 1.6 and 16 GHz. In addition to the dielectric measurements, the bulk density was measured for all the samples and the bulk chemical composition was determined for 56 of the samples. This study shows that ε\´ is frequency-independent over the range of 0.5-18 GHz for all rock samples, and that the bulk density ρ_b accounts for about 50% of the observed variance of ε\´. For silicate rocks, as much as 78% of the observed variance of ε\´ may be explained by the combination of density and the fractional contents of various oxides determined by X-ray fluorescence when the silicates are subgrouped by genesis. In contrast, the loss factor ε" decrease with increasing frequency for most rock samples. It was not possible to establish statistically significant relationships between ε" and the measured density of the rock samples. However, in the case of silicate rocks, 60% of the variance in ε" generally can be explained by the bulk chemical composition when the silicates are subgrouped by genesis