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| Titel |
Simulation study of Na-majorite |
| VerfasserIn |
A. Dymshits, V. Vinograd, N. Paulsen, B. Winkler, L. Perchuk, A. Bobrov |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250021772
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| Zusammenfassung |
| Garnets, which are found as inclusions in diamonds, often have the excess of Na2O and SiO2
[Stachel, 2001]. Experimental studies suggest that Na is incorporated in pyrope-rich garnet
via the coupled substitution Mg+Al=Na+Si [Bobrov et al., 2008]. This study is concerned
with the determination of the structure and the thermodynamic properties of NaGrt
(Na2MgSi5O12), which is assumed to be the end-member of pyrope-rich garnets with the
excess of Na2O and SiO2. Static lattice energy calculations were performed with
the program GULP [Gale & Rohl, 2003] using the force-field model [Vinograd et
al., 2007] for 200 structures of Na2MgSi5O12 composition. These structures were
prepared from Ia3-d pyrope Mg3Al2Si3O12 by replacing all octahedral Al atoms
with Si and 2/3 of Mg atoms with Na. The distribution of Mg and Na was varied
randomly. The static energies of these structures were cluster expanded using 8 pairwise
effective cluster interactions (ECI). The ECIs were used to constrain Monte Carlo
simulations within a 4×4×4 supercell (NNN exchangeable sites). The annealing
experiments have shown that the lowest energy structure has the space group I4 |
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