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Title: Enthalpy of mixing synthetic almandine-grossular and almandine-pyrope garnets from high-temperature solution calorimetry

Abstract

Enthalpy of solution measurements of synthetic garnet solid solutions on the joins Fe/sub 3/Al/sub 2/Si/sub 3/O/sub 12/ (almandine)-Ca/sub 3/Al/sub 2/Si/sub 3/O/sub 12/ (grossular) and Fe/sub 3/Al/sub 2/Si/sub 3/O/sub 12/-Mg/sub 3/Al/sub 2/Si/sub 3/O/sub 12/ (pyrope) have been made in eutectic (Li, Na)BO/sub 2/ at 760/sup 0/C. Garnets were prepared by high pressure, high temperature crystallization of homogeneous glasses and mechanical mixtures of end-member glasses and characterized by X-ray diffraction, microprobe analysis and Moessbauer resonance spectroscopy. Less than one percent of the total iron is ferric. The calorimetry shows that Ca, Fe/sup 2 +/ enthalpy of mixing in garnet is virtually zero, and that Mg, Fe/sup 2 +/ mixing is substantially non-ideal, with largest positive deviations near the almandine composition. These calorimetric results are not predictable from ionic size considerations, which would suggest ideality for Mg, Fe/sup 2 +/ mixing and considerable non-ideality for Ca, Fe/sup 2 +/ mixing. They are, however, consistent with predictions based on analysis of natural garnet occurrences. Apparently, subtle effects of X-site volume and distortion in garnet solid solutions produce important energetic effects not currently predictable from crystal chemistry. The present calorimetry, in conjunction with experimental phase equilibrium work, indicates that excess entropy in both solid solutionsmore » is very small.« less

Authors:
; ;
Publication Date:
Research Org.:
Univ. of Chicago, IL (USA)
OSTI Identifier:
6992568
Resource Type:
Journal Article
Journal Name:
Geochim. Cosmochim. Acta; (United States)
Additional Journal Information:
Journal Volume: 51:6
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; GARNETS; CALORIMETRY; CRYSTALLIZATION; ENTHALPY; GEOCHEMISTRY; CHEMICAL COMPOSITION; MASS SPECTROSCOPY; METAMORPHISM; MIXING; PETROGENESIS; PHASE STUDIES; SOLID SOLUTIONS; THERMODYNAMICS; X-RAY DIFFRACTION; CHEMISTRY; COHERENT SCATTERING; DIFFRACTION; DISPERSIONS; MINERALS; MIXTURES; OXYGEN COMPOUNDS; PHASE TRANSFORMATIONS; PHYSICAL PROPERTIES; SCATTERING; SILICATES; SILICON COMPOUNDS; SOLUTIONS; SPECTROSCOPY; THERMODYNAMIC PROPERTIES; 580400* - Geochemistry- (-1989)

Citation Formats

Geiger, C.A., Newton, R.C., and Kleppa, O.J. Enthalpy of mixing synthetic almandine-grossular and almandine-pyrope garnets from high-temperature solution calorimetry. United States: N. p., 1987. Web. doi:10.1016/0016-7037(87)90353-X.
Geiger, C.A., Newton, R.C., & Kleppa, O.J. Enthalpy of mixing synthetic almandine-grossular and almandine-pyrope garnets from high-temperature solution calorimetry. United States. doi:10.1016/0016-7037(87)90353-X.
Geiger, C.A., Newton, R.C., and Kleppa, O.J. Mon . "Enthalpy of mixing synthetic almandine-grossular and almandine-pyrope garnets from high-temperature solution calorimetry". United States. doi:10.1016/0016-7037(87)90353-X.
@article{osti_6992568,
title = {Enthalpy of mixing synthetic almandine-grossular and almandine-pyrope garnets from high-temperature solution calorimetry},
author = {Geiger, C.A. and Newton, R.C. and Kleppa, O.J.},
abstractNote = {Enthalpy of solution measurements of synthetic garnet solid solutions on the joins Fe/sub 3/Al/sub 2/Si/sub 3/O/sub 12/ (almandine)-Ca/sub 3/Al/sub 2/Si/sub 3/O/sub 12/ (grossular) and Fe/sub 3/Al/sub 2/Si/sub 3/O/sub 12/-Mg/sub 3/Al/sub 2/Si/sub 3/O/sub 12/ (pyrope) have been made in eutectic (Li, Na)BO/sub 2/ at 760/sup 0/C. Garnets were prepared by high pressure, high temperature crystallization of homogeneous glasses and mechanical mixtures of end-member glasses and characterized by X-ray diffraction, microprobe analysis and Moessbauer resonance spectroscopy. Less than one percent of the total iron is ferric. The calorimetry shows that Ca, Fe/sup 2 +/ enthalpy of mixing in garnet is virtually zero, and that Mg, Fe/sup 2 +/ mixing is substantially non-ideal, with largest positive deviations near the almandine composition. These calorimetric results are not predictable from ionic size considerations, which would suggest ideality for Mg, Fe/sup 2 +/ mixing and considerable non-ideality for Ca, Fe/sup 2 +/ mixing. They are, however, consistent with predictions based on analysis of natural garnet occurrences. Apparently, subtle effects of X-site volume and distortion in garnet solid solutions produce important energetic effects not currently predictable from crystal chemistry. The present calorimetry, in conjunction with experimental phase equilibrium work, indicates that excess entropy in both solid solutions is very small.},
doi = {10.1016/0016-7037(87)90353-X},
journal = {Geochim. Cosmochim. Acta; (United States)},
number = ,
volume = 51:6,
place = {United States},
year = {1987},
month = {6}
}