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Aluminium in quartz as an indicator of the temperature of formation of agate

Published online by Cambridge University Press:  05 July 2018

J. Götze*
Affiliation:
TU Bergakademie Freiberg, Institute of Mineralogy, D-09596 Freiberg, Germany
M. Plötze
Affiliation:
TU Bergakademie Freiberg, Institute of Mineralogy, D-09596 Freiberg, Germany
M. Tichomirowa
Affiliation:
TU Bergakademie Freiberg, Institute of Mineralogy, D-09596 Freiberg, Germany
H. Fuchs
Affiliation:
TU Bergakademie Freiberg, Institute of Mineralogy, D-09596 Freiberg, Germany
J. Pilot
Affiliation:
TU Bergakademie Freiberg, Institute of Mineralogy, D-09596 Freiberg, Germany
*

Abstract

An ‘Al-thermometer’ was applied to agate samples of volcanic parent rocks to provide information about the temperature of agate formation. The temperatures were calculated from concentrations of [AlO4]0 centres determined by electron paramagnetic resonance (EPR) measurements. The calculations for agate bands in some cases yield temperatures of up to 655°C, which are assumed to be invalid; they are thought to be artifacts resulting from non-equilibrium crystallization processes. In contrast, the formation temperatures (60–198°C) estimated for associated quartz incrustations within the agate geodes are in good accord with those calculated from oxygen isotope data. Direct estimation of the formation temperatures of agates is problematic. The best results will be obtained by analyses of associated phanerocrystalline quartz incrustations.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2001

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Footnotes

Present address: ETH Zurich, Institute of Geotechnical Engineering, CH-8093 Zurich, Switzerland

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