NASA TN D-6980 APPLICATION OF THERMODYNAMICS TO SILICATE CRYSTALLINE SOLUTIONS
i FOREWORD iii ACKNOWLEDGMENTS v SYMBOLS ix 1 THERMODYNAMIC RELATIONS IN CRYSTALLINE SOLUTIONS 1 2 THERMODYNAMIC STABILITY OF A SOLUTION 11 3 COMPOSITION OF COEXISTING PHASES 15 4 MEASUREMENT OF COMPONENT ACTIVITIES BY ANALYSIS OF PHASE DIAGRAMS 25 5 MEASUREMENT OF COMPONENT ACTIVITY USING COMPOSITION OF COEXISTING MINERALS 35 6 ORDER-DISORDER IN Fe-Mg SILICATES 39
Distribution of Magnesium and Iron between Orthopyroxene and Calcic Pyroxene in Natural Mineral Assemblages
Distribution coefficients with reference to Mg-Fe exchange and Mn-(Mg, Fe) exchange have been computed for sixty-four calcic pyroxene-orthopyroxene (or pigeonite) combinations from a variety of rocks. The distribution coefficient with reference to Mg-Fe exchange is denned as \documentclass{aastex}
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\begin{document}$$K_{D({\mathrm{Mg-Fe}})}\equiv\frac{X_{{\mathrm{MgSiO}}_{3}}}{1-X_{{\mathrm{MgSiO}}_{3}}} \cdot\frac{1-X_{{\mathrm{MgCaSi}}_{2}{\mathrm{O}}_{6}}}{X_{{\mathrm{MgCaSi}}_{2}{\mathrm{O}}_{6}}}$$\end{document}, where \documentclass{aastex}
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\begin{document}$$X_{{\mathrm{MgCaSi}}_{2}{\mathrm{O}}_{6}}$$\end{document} are mole fractions. In twenty-five high-grade metamorphic rocks the coefficient ranges from 0.51 to 0.65, and in fourteen rocks known or presumed to have crystallized from silicate melt, from 0.65 to 0.86. Two anomalous values were found. In ultramafic nodules in basaltic rock, the coefficient tends to approach unity more closely than in any other rocks. The distribution coefficient with reference to Mn-(Mg, Fe) exchange is variable to the extent that a correlation with temperature or pressure is not possible at present. A tentative equilibrium diagram may be constructed to illustrate the response of the Mg-Fe distribution coefficient to variations in temperature and pressure.
Elemental interplay: the production, circulation and deposition of Bronze Age metalwork in Britain and Ireland
Abstract This paper considers how people were compellingly engaged with, and drew upon, their elemental world in the Bronze Age (c. 2000 – 800 bc). It takes into account the production, circulation and deposition of metalwork and presents a number of themes concerned with the social construction of objects, places and people in the Bronze Age, while exploring how elements are drawn upon to facilitate this. The case study focuses on evidence from Britain and Ireland, although the interpretative themes presented can be applied to a wider geographical dataset. In particular, it considers how elements are interplayed in order to bring about and articulate wider social and material transformations taking place in the Bronze Age.