Phys Chem Minerals (1992) 19: 166-170

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Dielectric Constants of Topaz, Orthoclase and Scapolite and the Oxide Additivity Rule

Robert D. Shannon, Robert A. Oswald
Central Research and Development, Experimental Station 356/329

E.I. Du Pont de Nemours

Wilmington, DE 19880-0356, USA

George R. Rossman

Division of Geological and Planetary Sciences

California Institute of Technology

Pasadena, CA 91125, USA

#### Abstract

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

K'_{a =6.61 tan 6=0.0005
K'b = 6.82 tan 6=0.0007
K'c =6.81 tan 6=0.0007
}

orthoclase

K'_{a} =4.69 tan 6=0.0007

K'_{b} = 5.79 tan 6=0.0007
K'_{c} =5.63 tan 6=0.0011

K'_{11}=4.72

K_{22}=5.79

K'_{33}= 5.76

scapolite

K'a = 6.74 tan 6=0.0004

K'c =8.51 tan 6=0.0004

The deviation (C) between measured dielectric polarizabilities as determined from the Clausius-Mosotti equation and those calculated from the sum of ion polarizabilities according to aD(mineral)=SaD(ions) for topaz is 2.5%. The large deviations of orthoclase and scapolite from the oxide additivity rule with A = +7.2 and 1992), ± 17.6%, respectively, are attributed to "rattling" ions in orthoclase and "rattling" (Na,K,Ca) ions and disordered O= and Cl ions in scapolite.