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MnO exsolution in periclase from Långban, Sweden: an evaluation of the activity-composition relations in the system MgO–MnO

Published online by Cambridge University Press:  05 July 2018

J. P. R. de Villiers ,
P. R. Buseck  and
H. S. Steyn
J. P. R. de Villiers
Affiliation:
Mineralogy and Process Chemistry Division, Mintek, Randburg, 2125, South Africa
P. R. Buseck
Affiliation:
Departments of Geology and Chemistry, Arizona State University, Tempe, AZ 85287, USA
H. S. Steyn
Affiliation:
Department of Information Technology, Potchefstroom University, South Africa
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Abstract

The occurrence of MnO exsolution in periclase host crystals from Långban, Sweden, is described. The composition of the periclase is Mg0.942 Mn0.046Zn0.012O, and it coexists with exsolved manganosite crystals with a composition of Mn0.909Mg0.082Zn0.008O. Crystals of hausmannite are also present, indicating fO2 conditions approaching the MnO–Mn3O4 equilibrium.

Activity-composition data for the system MgO–MnO is critically reviewed. The data obtained from solid electrolyte measurements are rejected because of the unrealistic calculated equilibration temperatures and the large deviations from the gas equilibration Mn-Pt activity measurements. The large errors associated with the gas equilibration measurements, especially at large XMnO, also introduces uncertainties associated with the asymmetric interaction parameters. The non-parametric ‘jack-knife’ method was used to determine the asymmetric interaction parameters and their standard deviations from the data of Wood et al. (1994) and Tsai and Muan (1992). These were calculated as WMnO = 21.2 kJ/mol, σWMnO = 2.5 kJ/mol and WMgO = 8.2 kJ/mol, σWMgO = 3.3 kJ/mol.

Using the asymmetric interaction parameters, WMnO = 19.9 kJ/mol and WMgO = 13.7 kJ/mol for the system MgO–MnO as determined by Wood et al. (1994) and the equations for two-phase equilibrium as formulated by Thompson (1967), equilibration temperatures of 334°C and 466°C were calculated. The difference between the calculated temperatures is ascribed to inaccuracies in the experimentally determined interaction parameters.

Keywords

manganositepericlaseexsolutionsystem MgO–MnOcalculated solvus
Type
Research Article
Information
Mineralogical Magazine , Volume 62 , Issue 3 , June 1998 , pp. 333 - 339
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1998

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