Dielectric Constants of Apatite, Epidote, Vesuvianite, and Zoisite, and the Oxide Additivity Rule

Abstract

The dielectric constants and dielectric loss values of 4 Ca-containing minerals were determined at 1 MHz using a two-terminal method and empirically determined edge corrections. The results are: vesuvianitel κ′_a=9.93 tan δ=0.006 κ′_c=9.79 tan δ=0.005 vesuvianitel κ′_a=10.02 tan δ=0.002 κ′_c=9.85 tan δ=0.003 zoisite1 κ′_a =10.49 tan δ=0.0006 κ′_b =15.31 tan δ=0.0008 κ′_c=9.51 tan δ=0.0008 zoisite2 κ′_a =10.55 tan δ=0.0011 κ′_b =15.45 tan δ=0.0013 κ′_c=9.39 tan δ=0.0008 epidote κ′_(11)= 9.52 tan δ=0.0008 κ′_(22)=17.1 tan δ=0.0009 κ′_(33)= 9.37 tan δ=0.0006 fluorapatite1 κ′_a =10.48 tan δ=0.0008 κ′_c = 8.72 tan δ=0.0114 fluorapatite2 κ′_a =10.40 tan δ=0.0010 κ′_c=8.26 tan δ=0.0178 The deviation (δ) between measured dielectric polarizabilities as determined from the Clausius-Mosotti equation and those calculated from the sum of oxide polarizabilities according to α_D (mineral)=∑ α_D (oxides) for vesuvianite is ∼ 0.5%. The large deviations of epidote and zoisite from the additivity rule with Δ=+ 10.1 and + 11.7%, respectively, are attributed to "rattling" Ca ions. The combined effects of both a large F thermal parameter and possible F-ion conductivity in fluorapatite are believed to be responsible for Δ=+2–3%. Although variation of oxygen polarizability with oxygen molar volume (V_o) is believed to affect the total polarizabilities, the variation of V_o in these Ca minerals is too small to observe the effect.

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