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Crystal chemistry of aegirine as an indicator of P-T conditions

Published online by Cambridge University Press:  05 July 2018

L. Secco ,
A. Guastoni ,
F. Nestola ,
G. J. Redhammer  and
A. Dal Negro
L. Secco*
Affiliation:
Dipartimento di Geoscienze, Università di Padova, Corso Garibaldi 37, I-35137, Padova, Italy
A. Guastoni
Affiliation:
Dipartimento di Geoscienze, Università di Padova, Corso Garibaldi 37, I-35137, Padova, Italy
F. Nestola
Affiliation:
Dipartimento di Geoscienze, Università di Padova, Corso Garibaldi 37, I-35137, Padova, Italy
G. J. Redhammer
Affiliation:
Department of Materials Engineering and Physics, Division of Mineralogy, University of Salzburg, Hellbrunnerstr. 34, A-5020 Salzburg, Austria
A. Dal Negro
Affiliation:
Dipartimento di Geoscienze, Università di Padova, Corso Garibaldi 37, I-35137, Padova, Italy
*
*E-mail: [email protected]
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Abstract

One metamorphic and four magmatic aegirines, together with two end-member aegirines synthesized at atmospheric pressure and different temperatures, were investigated by single-crystal X-ray diffraction. The limited compositional differences allow the polyhedral volumes to be almost constant in all the aegirines investigated( VM1 ≈ 11.0 Å3; VM2 ≈ 26.3 Å3; VT ≈ 2.21 Å3). However, differences in polyhedral distortions are responsible for the cell-volume variations, reflected mainly in the change of a and β cell parameters. Cell volume is only partly related to the composition of these aegirines: with increasing formation temperature, an increase in the unit-cell volume of ~1.2 Å3 is observed, while a significant contraction of the cell volume occurs during high-pressure formation. As the difference in cell volume between the two synthetic aegirines is ascribed to the different conditions of synthesis temperature, the same interpretation could be adopted for the differences observed in natural aegirines.

Keywords

clinopyroxeneX-ray diffractionsingle-crystalaegirine
Type
Research Article
Information
Mineralogical Magazine , Volume 71 , Issue 3 , June 2007 , pp. 321 - 326
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2007

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