R.D. Shannon, M.A. Subramanian
E. I. Du Pont de Nemours and Co., Inc., Central
Research and Development Department,
Experimental Station, Wilmington, DE 19880-0356, U.S.A.
S. Hosoya
Institute for Materials Research, Tohoku University, Katsura 2-1-1
Sendai 980, Japan
G.R. ROSSMAN
Division of Geological and Planetary Sciences
California Institute of Technology, Pasadena, CA 91125-2500, U.S.A
tephroite κ'a = 8.79 κ'b = 10.20 κ'c = 8.94 fayalite κ'a = 8.80 κ'b = 8.92 κ'c = 8.58 olivine κ'a = 7.16 κ'b = 7.61 κ'c = 7.03 |
tan δa = 0.0006 tan δb = 0.0006 tan δc = 0.0008 tan δa = 0.0004 tan δb = 0.0018 tan δc = 0.0010 tan δa = 0.0006 tan δb = 0.0008 tan δc = 0.0006 |
The low dielectric constant and loss of the fayalite indicate an exceptionally low Fe^{3+} content. An FeO polarizability of 4.18 Å^{3}, determined from a_{D}(FeO) = [a_{D}(Fe_{2}SiO_{4}) - a_{D}(SiO_{2})]/2, is probably a more reliable value for stoichiometric FeO than could be obtained from Fe_{x}O where x = 0.90-0.95. The agreement between measured dielectric polarizabilities as determined from the Clausius-Mosotti equation and those calculated from the sum of oxide polarizabilities according to a_{D}(M_{2}M'X_{4}) = 2a_{D}(MX) + a_{D}(M'X_{2}) is ~ +2.8% for tephroite and + 0.2% for olivine. The deviation from additivity in tephroite is discussed.
Phys Chem Minerals (1991) 18:1-6