Elastic strain enthalpies of exsolution: HF solution calorimetric experiments on alkali aluminosilicate and aluminogermanate feldspars

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 degreesC for chemically homogeneous unstrained members of this series can be expressed as a function of mole fraction K (N-OrGe): -H-soln (kJ/mol) = 630.65 + 9.92 N-OrGe - 47.0 N-OrGe(2) + 17.6 N-orGe(3). The associated enthalpies of mixing, H-ex (kJ/mol) = 29.4 N-OrGe N-AbGe(2) + 11.9 N-AbGe N-OrGe(2) (where N-AbGe 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.

Title	Elastic strain enthalpies of exsolution: HF solution calorimetric experiments on alkali aluminosilicate and aluminogermanate feldspars
Creator	Yund, R. A.
	Breit, U.
	Kroll, H.
	Hovis, Guy L.
Publisher	American Mineralogist
Academic Department	Geology & Environmental Geosciences
Division	Natural Sciences
Organization	Lafayette College
Date Issued	April 2003
Date Available	2013-02-05T20:36:22Z
Type	Article
Language	English
Bibliographic Citation	Hovis, G. L., et al. (2003 Apr.) "Elastic strain enthalpies of exsolution: HF solution calorimetric experiments on alkali aluminosilicate and aluminogermanate feldspars." American Mineralogist 88 (4): 547-555.
Standard Identifier	Handle 10385/1084
Permalink	http://hdl.handle.net/10385/1084
Rights Statement	In Copyright
Rights Holders	Mineralogical Society of America