Cookeite LiAl4(Si3Al)O10(OH)8: Experimental study and thermodynamical analysis of its compatibility relations in the Li2O?Al2O3?SiO2?H2O system |
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| Authors: | Olivier Vidal Bruno Goffé |
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| Institution: | 1. Institut für Mineralogie, Ruhr-Universit?t Bochum, Postfach 1021 48, W-4630, Bochum, FRG
2. Laboratoire de Géologie, Ecole Normale Supérieure, 24 rue Lhomond, F-75005, Paris
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| Abstract: | Three reactions limiting the stability field of the di-trioctahedral chlorite cookeite in the presence of quartz, in the system
Li2O−Al2O3−SiO2−H2O (LASH) have been reversed in the range 290–480°C, 0.8–14 kbar, using natural material close to the end member composition.
Combining our results with known and estimated thermodynamic properties of the other minerals belonging to the LASH system,
the enthalpy (-8512200 J/mol) and the entropy (504.8 J/mol*K) of cookeite are calculated by a feasible solution space approach. The knowledge of these values allowed us to draw the
first P−T phase diagram involving both the hydrated Li-aluminosilicates cookeite and bikitaite, which is applicable to a large
variety of natural rock systems. The low thermal extent of the stability field of cookeite+quartz (260–480°C) makes cookeite
a valuable indicator of low temperature conditions within a wide range of pressure (1–14 kbar). |
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