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American Mineralogist; April 2003; v. 88; no. 4; p. 547-555
© 2003 Mineralogical Society of America
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Elastic strain enthalpies of exsolution: HF solution calorimetric experiments on alkali aluminosilicate and aluminogermanate feldspars

Guy L. Hovis1, Herbert Kroll2, Udo Breit2 and Richard A. Yund3

1 Department of Geology and Environmental Geosciences, Lafayette College, Easton, Pennsylvania 18042, U.S.A.
2 Institut für Mineralogie, Universität Münster, D-48149 Münster, Germany
3 Department of Geological Sciences, Brown University, Providence, Rhode Island 02912, U.S.A.

Correspondence: * E-mail: hovisguy{at}lafayette.edu

A new series of aluminogermanate alkali feldspars has been synthesized as part of a study to investigate elastic strain energies in exsolved samples. Enthalpies of solution in 20.1 wt% hydrofluoric acid (HF) at 50 °C for chemically homogeneous unstrained members of this series can be expressed as a function of mole fraction K (NOrGe): –Hsoln (kJ/mol) = 630.65 + 9.92 NOrGe – 47.0 NOrGe2 + 17.6 NOrGe3. The associated enthalpies of mixing, Hex (kJ/mol) = 29.4 NOrGe N2AbGe + 11.9 NAbGe N2OrGe (where NAbGe is mole fraction Na), reach maximum values of 5.4 kJ/mol at sodic compositions, similar in behavior to normal aluminosilicate analogs.

Enthalpies of elastic strain associated with exsolution have been determined via HF solution calorimetric experiments on several coherently exsolved samples of the aluminogermanate series and also on a normal Ge-free aluminosilicate alkali feldspar. These energies were found to be less than 2.0 kJ/ mol, consistent with independent estimates by previous workers.




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R. Abart, E. Petrishcheva, R. Wirth, and D. Rhede
Exsolution by spinodal decomposition II: Perthite formation during slow cooling of anatexites from Ngoronghoro, Tanzania
Am J Sci, June 1, 2009; 309(6): 450 - 475.
[Abstract] [Full Text] [PDF]


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