The Dielectric Permittivity of Calcite and Arid Zone Soils with Carbonate Minerals

phases (solid, liquid, and gas) are known, especially if the model is to be used to predict water content or Measurement of soil dielectric properties, ε are widely used to porosity. The permittivity of air and water are well docuestimate water content in soils from remote sensing and from in situ soil sensors such as time domain reflectometry (TDR). The mineral mented (Lide, 1999). However, a value of 5 reflecting permittivity also plays an important role in geochemical dissolution the permittivity of quartz (4.19 to 5.00; Keller, 1989) is and precipitation. Models used to estimate water content from soils often used as an input parameter for the permittivity often assume a value of 5 for the mineral permittivity εs. However, of the solid for modeling (Friedman, 1998). calcite (CaCO3), a major constituent of some arid and semi-arid soils, has a permittivity of 8 to 9, nearly twice the permittivity of quartz Geochemical Importance of the (εs 4.6). We studied four soils, with micaceous mineralogy, but with Mineral Permittivity two soils having approximately 40% calcite. We also measured the permittivity of Iceland Spar calcite (εs 9.1) and a microcrystalline Water is an excellent solvent, primarily because of its calcite (εs 8.3), and use atomistic modeling to account for differences high dielectric constant, approximately 80. For a continin permittivity based on the crystal density. We found permittivities uum scale analysis, the inverse square Coulomb force for our soils to be in the range of 5.8 to 6.6, higher calcite contents between two charged atoms is reduced by a factor deterresulting in increased permittivity. The estimated permittivity of the mined by the permittivity of the medium surrounding calcite in the soils was 7.4 to 7.9, lower than the highly crystalline them. The free energy, w(r) of the Coulomb interaction samples. We estimate, for a soil with a porosity of 0.5 that assuming between two charges Q1 and Q2 is: a permittivity of 5 instead of 6.6 will result in an overestimation of water content of about 1% at saturation. This demonstrates that a large quantity of pedogenic calcite (40%) in soil is unlikely to cause w(r) Q1Q2 4 εoεer [1] substantial error in the determination of water content using standard calibration equations. However, the lower dielectric permittivity prewhere εe is the permittivity of the surrounding or envidicted for pedogenic calcite may have consequences for the interpretaronment, εo is the permittivity of free space (8.854 pF tion and understanding of geochemical processes. m 1) and r is the distance between the two charges. This indicates the importance of the permittivity of the environment in determining how the charges feel each T development of electromagnetic sensor techother. A step further takes us to the Born or solvation nology toward the end of the last century increased energy of an ion ( i). The Born energy, a positive quaninterest in the measurement of soil properties using tity, gives the electrostatic free energy of an ion in a electromagnetic techniques. The determination of soil medium of permittivity εe: water content from the measurement of soil dielectric permittivity has become a widely accepted method