Dielectric constants of topaz,orthoclase and scapolite and the oxide additivity rule

The dielectric constants and dissipation factors of topaz, scapolite and orthoclase were determined at 1 MHz using a two-terminal method and empirically determined edge corrections. The results are: topaz κ′ _a =6.61 tan δ=0.0005 κ′ _b =6.82 tan δ=0.0007 κ′ _c =6.81 tan δ=0.0007 orthoclase κ′ _a =4.69 tan δ=0.0007 κ′ _b =5.79 tan δ=0.0007 κ′ _c =5.63 tan δ=0.0011 κ′ ₁₁ =4.72 κ′ ₂₂ =5.79 κ′ ₃₃ =5.76 scapolite κ′ _a =6.74 tan δ=0.0004 κ′ _c =8.51 tan δ=0.0004 The deviation (Δ) between measured dielectric polarizabilities as determined from the Clausius-Mosotti equation and those calculated from the sum of ion polarizabilities according to α _D (mineral)=∑α_D (ions) for topaz is 2.5%. The large deviations of orthoclase and scapolite from the oxide additivity rule with δ=+7.2 and + 17.6%, respectively, are attributed to “rattling” K ions in orthoclase and “rattling” (Na,K,Ca) ions and disordered O⁼ and Cl^- ions in scapolite.