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An ESR and calorimetric study of iron oolitic samples from the Northampton ironstone

Published online by Cambridge University Press:  09 July 2018

A. U. Gehring
Affiliation:
Institut für Geophysik, ETH-Hönggerberg, CH-8093 Zürich
R. Karthein
Affiliation:
Laboratorium für Physikalische Chemie der ETH, CH-8092 Zürich, Switzerland

Abstract

Electron spin resonance (ESR) spectroscopy and calorimetric methods were used to characterize conversion processes in multimineral samples from the Northampton ironstone (NIS) at temperatures between 25°C and 800°C. The beginning of the thermal conversion processes can be determined by the formation of asymmetric ESR spectra with g ≈ 2 at 250°C. The breakdown of the berthierine structure between 250°C and 520°C is indicated by the disappearance of the hyperfine splitting in the Mn2+ spectrum and the formation of magnetite. The decomposition of siderite and calcite was found by calorimetric methods at 580°C and 700°C, respectively. The hematite formation between 550°C and 800°C is explained by the decomposition of siderite but also by the oxidation of previously formed magnetite. The occurrence of hematite as the dominant ferric oxide at 800°C signifies the end of the conversion process of the major mineral phases in the NIS samples.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1990

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