Elastic Properties of Pyrope


Bridget O'Neill, Jay D. Bass

Department of Geology
University of Illinois, 1301 W. Green St. Urbana, IL 61801, USA

George R. Rossman

Division of Geological and Planetary Sciences
California Institute of Technology, Pasadena, CA 91125, USA

Charles A. Geiger and Klaus Langer

Institut für Mineralogie und Kristallographie
Technische Universität Berlin, Ernst Reuter Platz 1
W-1000 Berlin 12, Federal Republic of Germany

Abstract

Brillouin spectroscopy was used to measure the single crystal elastic properties of a pure synthetic pyrope and a natural garnet containing 89.9 mol% of the pyrope end member (Mg3Al2Si3O12). The elastic moduli, cij, of the two samples are entirely consistent and agree with previous estimates of the elastic proper ties of pyrope based upon the moduli of solid solutions. Our results indicate that the elastic moduli of pyrope end-member are c11 = 296 2 ± 05, c12 = 111.1 ± 06, c44=91.6 ± 03, Ks=172.8 ± 0.3, m = 92.0 ± 0.2, all in units of GPa. These results differ by several percent from those reported previously for synthetic pyrope, but are based upon a much larger data set. Although the hydrous components of the two samples from the present study are substantially different, representing both 'dry' and 'saturated' samples, we find no discernable effect of structurally bound water on the elastic properties. This is due to the small absolute solubility of water in pyrope, as compared with other garnets such as grossular.

Physics and Chemistry of Minerals (1991) 17:617-621