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Thermodynamic properties of tremolite: A correction and some comments
-
Bernard W. Evans
,
Mark S. Ghiorso
Published/Copyright:
March 26, 2015
Abstract
Microprobe analysis of tremolite from “St. Gotthard,” Switzerland, shows that it is close to endmember in composition (Ca = 1.97 apfu), and not hypercalcic (Ca = 2.16 apfu), as a previous wetchemical analysis suggested. The latter formula, and a corresponding thermodynamic activity (0.67), were used in the experimental database for the extraction of an optimal set of thermodynamic properties for tremolite (Chernosky et al. 1998). We derive a revised enthalpy of formation of tremolite (-12307.9 kJ/mol) based on bracketing experiments for the breakdown reactions of tremolite and tremolite + forsterite, and the assumption of time-averaged effective equilibrium compositions of phases in the experimental charges. Mg-cummingtonite substitution in tremolite is accommodated during free-energy minimization calculations by allowing the stoichiometry of the standard-state reaction to vary with the changing bulk composition of the amphibole. The breakdown temperature of tremolite is lowered with increasing cummingtonite component. Our procedure also allows continuous variation in the equilibrium compositions and activities of pyroxene and amphibole phasecomponents with P and T.
Received: 1999-6-10
Accepted: 1999-10-15
Published Online: 2015-3-26
Published in Print: 2000-4-1
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
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- A crystal chemical re-evaluation of amphibole/melt and amphibole/clinopyroxene DTi values in petrogenetic studies
- Mineralogy of mafic xenoliths and their reaction zones in the olivine lamproite from Prairie Creek Arkansas and the paragenesis of haggertyite, Ba [Fe6Ti5Mg]O19
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- Spectroscopic and structural properties of synthetic micas on the annite-siderophyllite binary: Synthesis, crystal structure refinement, Mössbauer, and infrared spectroscopy
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- Diffusion of C and O in calcite at 100 MPa
- Solubility and stability of zeolites in aqueous solution: II. Calcic clinoptilolite and mordenite
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