Equilibria in the Mg-rich Part of the Pyroxene Quadrilateral

G. A. Jenner* and D. H. Green
Department of Geology, University of Tasmania, Hobart, Tasmania, Australia, 7001
*Present address: Max-Planck Institut für Chemie, Saarstrasse 23, Postfach 3060, D-6500 Mainz, West Germany.

Abstract: Pyroxene phase relations in the Mg-rich corner of the pyroxene quadrilateral, at 1 atmosphere, have been reinvestigated. Experimental studies on sixteen selected compositions in the systems CMS and CFMS were undertaken in the temperature range 1100–1400 °C. The results of this study clarify our understanding of the pyroxene stability relations at low pressure. In particular, the demonstration that there is a hightemperature stability field of orthoenstatite denies the existence of a stable (or real) invariant point defined by the reactions OE = PE + DI, PE + DI = PI, and OE + DI = PI, in the system CaMgSi2O6-Mg2Si2O6. New phase relations, consistent with the experimental findings of this and other studies, for the Mg-rich corner of the pyroxene quadrilateral are presented. These new phase relations may be of use in interpreting the origin of volcanic rocks containing magnesian pigeonite.

Mineralogical Magazine; June 1983 v. 47; no. 343; p. 153-160; DOI: 10.1180/minmag.1983.047.343.05
© 1983, The Mineralogical Society
Mineralogical Society (www.minersoc.org)