Phys Chem Minerals (1992) 19: 166-170

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


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:

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

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'33= 5.76

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.