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Contributions to Mineralogy and Petrology

, Volume 67, Issue 4, pp 397–404 | Cite as

Thermodynamic properties of almandine-grossular garnet solid solutions

  • G. Cressey
  • R. Schmid
  • B. J. Wood
Article

Abstract

The mixing properties of Fe3Al2Si3O12-Ca3Al2Si3O12 garnet solid solutions have been studied in the temperature range 850–1100° C. The experimental method involves measuring the composition of garnet in equilibrium with an assemblage in which the activity of the Ca3Al2Si3O12 component is fixed. Experiments on the assemblage garnet solid solution, anorthite, Al2SiO5 polymorph and quartz at known pressure and temperature fix the activity of the Ca3Al2Si3O12 component through the equilibrium:
$$\begin{gathered} {\text{3CaAl}}_{\text{2}} {\text{Si}}_{\text{2}} {\text{O}}_{\text{8}} \rightleftarrows {\text{Ca}}_{\text{3}} {\text{Al}}_{\text{2}} {\text{Si}}_{\text{3}} {\text{O}}_{{\text{12}}} \hfill \\ {\text{Anorthite garnet}} \hfill \\ {\text{ + 2Al}}_{\text{2}} {\text{SiO}}_{\text{5}} {\text{ + SiO}}_{\text{2}} \hfill \\ {\text{ sillimanite/kyanite quartz}}{\text{.}} \hfill \\ \end{gathered}$$
(1)
This equilibrium, with either sillimanite or kyanite as the aluminosilicate mineral, was used to control \({\text{a}}_{{\text{Ca}}_{\text{3}} {\text{Al}}_{\text{2}} {\text{Si}}_{\text{3}} {\text{O}}_{{\text{12}}} }^{{\text{gt}}} \). The compositions of the garnet solutions produced were determined by measurement of their unit cell edges.

At 1 bar Fe3Al2Si3O12-Ca3Al2Si3O12 garnets exhibit negative deviations from ideality at the Fe-rich end of the series and positive deviations at the calcium end. With increasing pressure the activity coefficients for the Ca3Al2Si3O12 component increase because the partial molar volume of this component is greater than the molar volume of pure grossular. Previous studies indicate that the activity coefficients for the Ca3Al2Si3O12 component also increase with increasing (Mg/Mg+Fe) ratio of the garnet.

The region of negative deviation from ideality implies a tendency towards formation of a stable Fe-Ca garnet component. Evidence in support of this conclusion has been found in a natural Fe-rich garnet which was found to contain two different garnet phases of distinctly different compositions.

Keywords

Molar Volume Activity Coefficient Aluminosilicate Negative Deviation Kyanite 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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References

  1. Birch, F., Compressibility; elastic constants. In: Handbook of Physical Constants (S.P. Clark, Jr. Ed.) Geol. Soc. Am. Mem. 97, 97–173 (1966)Google Scholar
  2. Boyd, F.R., England, J.L.: Apparatus for phase-equilibria measurements at pressures up to 50kb and temperatures up to 1750 °C. J. Geophys. Res. 65, 741–748 (1960)Google Scholar
  3. Chinner, G.A., Boyd, F.R., England, J.L.: Physical properties of garnet solid solutions. Carnegie Inst. Wash. Year Book, 59, 76–78 (1960)Google Scholar
  4. Cressey, G.: Exsolution in almandine-pyrope-grossular garnet. Nature 271, 533–534 (1978)Google Scholar
  5. Darken, L.S., Gurry, R.W.: Physical Chemistry of Metals, New York, McGraw-Hill (1953)Google Scholar
  6. Ganguly, J.: The energetics of natural garnet solid solution. II. Mixing of the calcium silicate end-members. Contrib. Mineral. Petrol. 55, 81–90 (1976)Google Scholar
  7. Ganguly, J., Kennedy, G.C.: The energetics of natural garnet solid solution. I. Mixing of the aluminosilicate end-members. Contrib. Mineral. Petrol. 48, 137–148 (1974)Google Scholar
  8. Hariya, Y., Kennedy, G.C.: Equilibrium study of anorthite under high pressure and high temperature. Am. J. Sci., 266, 193–203 (1968)Google Scholar
  9. Hensen, B.J., Schmid, R., Wood, B.J.: Activity-composition relationships for pyrope-grossular garnet. Contrib. Mineral. Petrol. 51, 161–166 (1975)Google Scholar
  10. Holdaway, M.J.: Stability of andalusite and the aluminium silicate phase diagram. Am. J. Sci. 271, 97–131 (1971)Google Scholar
  11. Hsu, L.C.: Selected phase relationships in the system Al-Mn-Fe-Si-O-H: A model for garnet equilibria. J. Petrol. 9, 40–83 (1968)Google Scholar
  12. Johannes, W., Bell, P.M., Mao, H.K., Boettcher, A.L., Chipman, D.W., Hays, J.F., Newton, R.C., Seifert, F.: An interlaboratory comparison of piston-cylinder pressure calibration using the albite breakdown reaction. Contrib. Mineral. Petrol. 32, 24–38 (1971)Google Scholar
  13. Newton, R.C., Charlu, T.V., Kleppa, O.J.: Thermochemistry of high pressure garnets and clinopyroxenes in the system CaO-MgO-Al2O3-SiO2. Geochim. Cosmochim. Acta, 41, 369–377 (1977)CrossRefGoogle Scholar
  14. Robie, R.A., Bethke, P.M., Toulmin, M.S., Edwards, J.L.: X-ray crystallographic data, densities and molar volumes of minerals. In: Handbook of Physical Constants (S.P. Clark, Jr., ed.) Geol. Soc. Am. Mem. 97, 27–73 (1966)Google Scholar
  15. Robie, R.A., Waldbaum, D.R.: Thermodynamic properties of minerals and related substances at 298.15 °K (25.0 °C) and one atmosphere (1.013 bars) pressure and at higher temperatures. U.S. Geol. Surv. Bull. 1259, 256p. (1968)Google Scholar
  16. Saxena, S.K.: Distribution of elements between co-existing minerals and the nature of solid solution in garnet. Am. Mineral. 53, 994–1014 (1968)Google Scholar
  17. Schmid, R., Cressey, G., Wood, B.J.: Experimental determination of univariant equilibria using divariant solid solution assemblages. Am. Min. (in press), 1978Google Scholar
  18. Skinner, B.J.: Physical properties of end-members of the garnet group. Am. Mineral. 41, 428–436 (1956)Google Scholar
  19. Skinner, B.J.: Thermal expansion. In: Handbook of Physical Constants (S.P. Clark, Jr., ed.) Geol. Soc. Am. Mem. 97, 75–96 (1966)Google Scholar
  20. Wood, B.J., Fraser, D.G.: Elementary thermodynamics for geologists. Oxford University Press, 1976Google Scholar
  21. Yoder, H.S., Jr.: Almandite garnet stability range. (abstract) Am. Mineral. 40, 342 (1955)Google Scholar

Copyright information

© Springer-Verlag 1978

Authors and Affiliations

  • G. Cressey
    • 1
  • R. Schmid
    • 1
  • B. J. Wood
    • 1
  1. 1.Department of GeologyUniversity of ManchesterManchesterEngland

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