caa a22 4500 46579159X CHVBK 20180323112026.0 cr unu---uuuuu 170327e19900901xx s 000 0 eng 10.1007/BF00286831 doi (NATIONALLICENCE)springer-10.1007/BF00286831 Holland Timothy Department of Earth Sciences, Cambridge University, Downing Street, CB2 3EQ, Cambridge, UK aut Activities of components in omphacitic solid solutions [Elektronische Daten] An application of Landau theory to mixtures [Timothy Holland] Available experimental data on mixing of disordered C2/c clinopyroxenes in the system diopside-jadeite-hedenbergite-acmite are reviewed and evaluated. Because the methods used to determine jadeite activity suffer from severe uncertainty at high jadeite mol fractions, these data cannot be used to infer asymmetry in the jadeite-diopside or the jadeite-hedenbergite solid solutions. If the measurement uncertainties are taken into account, a single parameter (regular, or reciprocal energy) suffices to describe the mixing properties of these two solid solutions. It is argued that a two-site entropy of mixing satisfies the experiments and is consistent with the C2/c disordered nature of the solid solutions; the data in the range 600-1300° C are consistent with a temperature-independent interaction energy, implying no discernible excess entropy. The available experimental data imply W=26±2 kJ mol−1 for jd-di, and W=25±3 kJ mol−1 for jd-hd, solid-solutions. Landau theory for a tricritical phase transformation (C2/c-P2/n) is in good agreement with the calorimetrically determined disordering enthalpy, and may be used to derive a simple expression for the activities in ordered omphacite solid solutions. The derived activities of jadeite at 600° C in ordered omphacites are remarkably close to those reported previously for short-range ordered pyroxenes. A simple model is presented for determining the activities of end-members in the system jadeite-diopside-hedenbergite-acmite. Springer-Verlag, 1990 Contributions to Mineralogy and Petrology Springer-Verlag 105/4(1990-09-01), 446-453 0010-7999 105:4<446 1990 105 410 https://doi.org/10.1007/BF00286831 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/BF00286831 text/html Onlinezugriff via DOI NATIONALLICENCE 100 1- Holland Timothy Department of Earth Sciences, Cambridge University, Downing Street, CB2 3EQ, Cambridge, UK aut NATIONALLICENCE 773 0- Contributions to Mineralogy and Petrology Springer-Verlag 105/4(1990-09-01), 446-453 0010-7999 105:4<446 1990 105 410 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer