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Uncertainties on elastic parameters and occupancy factors: how do they affect the accuracy of the calculated Gibbs energy of minerals at ( P , T ) conditions? The case of 3 T - versus 2 M 1-phengite.
- Source :
- Physics & Chemistry of Minerals; Nov2007, Vol. 34 Issue 9, p637-645, 9p
- Publication Year :
- 2007
-
Abstract
- Abstract  The present paper reports a study about how the uncertainties on some fundamental thermodynamic and structural quantities (formation enthalpy, specific heat, thermo-elastic properties, occupancy factors) propagate and affect the Gibbs energy calculated at given pressure and temperature conditions [G(P,T)] for mineral phases. A particular attention is paid to the role played by the uncertainties on the bulk modulus, its first derivative versus pressure, molar volume at a reference condition, i.e. V 0, and occupancy factors. The calculations in question are carried out for three phases: 2M 1-phengite, olivine and MgAl-spinel, in order to provide coverage for thermo-elastic parameters values common in a variety of natural processes. Above a few GPa, the uncertainty due to the deformation energy, i.e. Ï[ÎG deform], and dependent on the parameters governing the equation of state, grows the dominant contribution to the total uncertainty on G(P,T), i.e. Ï[G(P,T)]. Ï[ÎG deform] is very sensitive to V 0, but the comparatively small Ï(V 0)/V 0 value makes the V 0-contribution to Ï[ÎG deform] less relevant than those due to the elastic parameters. The stability curve of 3T- versus 2M 1-phengite as a function of pressure (Curetti et al. in Phys Chem Mineral 32:670â678, 2006) is here revised in the light of the uncertainty on G(P,T): an improvement of accuracy such as to reduce the uncertainty on bulk modulus and its first derivative versus pressure by a 0.05 factor is, in principle, required to guarantee a fully unambiguous description of the relative stability between these two phases. [ABSTRACT FROM AUTHOR]
- Subjects :
- ROCK-forming minerals
MINERALS
GEMS & precious stones
MATERIALS
Subjects
Details
- Language :
- English
- ISSN :
- 03421791
- Volume :
- 34
- Issue :
- 9
- Database :
- Complementary Index
- Journal :
- Physics & Chemistry of Minerals
- Publication Type :
- Academic Journal
- Accession number :
- 27319059