Heat capacity and entropy of low structural state plagioclases

The heat capacity of 11 different compositions of the low structural state plagioclase binary was measured between 5 and 773 K. The results are compared to those obtained from synthetic high structural state samples investigated in a previous study and obtained from a heat-treated natural sample of...

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Bibliographic Details
Published in:Physics and chemistry of minerals 2013-02, Vol.40 (2), p.167-173
Main Authors: Benisek, A., Dachs, E., Carpenter, M. A.
Format: Article
Language:English
Subjects:
Anorthite
Composition
Crystallography and Scattering Methods
Earth and Environmental Science
Earth Sciences
Entropy
Geochemistry
Gold
Heat treatment
High temperature
Mineral Resources
Mineralogy
Order parameters
Original Paper
Phase transitions
Plagioclase
Specific heat
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Summary:The heat capacity of 11 different compositions of the low structural state plagioclase binary was measured between 5 and 773 K. The results are compared to those obtained from synthetic high structural state samples investigated in a previous study and obtained from a heat-treated natural sample of this study. The heat capacity of anorthite samples with slightly different order parameters shows large differences at ~500 K, where the Ibar1-Pbar1 phase transition occurs, which affects petrological calculations. At T  = 298.15 K, the vibrational entropy versus composition behaviour of the low structural state plagioclases is almost ideal, in contrast to the high structural state plagioclases with positive excess vibrational entropies. At higher temperatures, the low structural state plagioclases show a negative deviation from ideal vibrational entropy composition behaviour in the Na-rich region.
ISSN:0342-1791
1432-2021
DOI:10.1007/s00269-012-0556-2