Mixing properties and stability of jadeite-acmite pyroxene in the presence of albite and quartz

The stability of synthetic jadeite-acmite pyroxene coexisting with albite and quartz has been determined at 600, 700, and 900?? C. The end-member reaction: albite = jadeite + quartz has been determined to lie between 1.67 and 1.70 GPa at 600?? C, 1.88 and 1.90 GPa at 700?? C, and 2.44 and 2.48 GPa at 900?? C. Jd78Acm22 + quartz is stable above 1.58, 1.78, and 2.33 GPa at 600, 700, and 900?? C, respectively. Jd61Acm39 + quartz is stable above 1.47, 1.67, and 2.18 GPa at 600, 700, and 900?? C, respectively. Addition of as much as 40% of acmite component in jadeite extends pyroxene stability by less than 300 MPa at 900?? C. Unit-cell parameters measured for synthetic jadeite-acmite pyroxenes indicate linear volume-composition relations. The data are consistent with ideal mixing in jadeite-acmite solutions. ?? 1995 Springer-Verlag.