Preferred Orientation of Experimentally Deformed Pyrite Measured by Means of Neutron Diffraction

H. Siemes, D. Zilles, S. F. Cox, P. Merz, W. Schäfer, G. Will, H. Schaeben and K. Kunze
Institut für Mineralogie und Lagerstättenlehre, RWTH Aachen, 5100 Aachen, Germany
Research School of Earth Sciences, Australian National University, Canberra ACT 2601, Australia
Mineralogisches Institut, Universität Bonn, Außenstelle Forschungszentrum Jülich (KFA), 5170 Jülich, Germany
Laboratoire de Metallurgie des Materiaux Polycristallins (LM2P), Universite de Metz, 57045 Metz, France
Brigham Young University, Dept. of Manufacturing Engineering, Provo, UT 84602, USA

Abstract: Neutron diffraction texture goniometry indicates that naturally deformed polycrystalline pyrite ores from Mt. Lyell (Tasmania) and Degtiarka (Ural Mountains) have weak lattice preferred orientations. During experimental deformation involving dislocation flow at elevated temperatures and pressures, these initial fabrics have been modified to produce new lattice preferred orientations.

Polycrystalline pyrite form Mt. Lyell (B-1) has an initial <111>-fibre texture perpendicular to a grain-size layering. After 24% shortening perpendicular to the <111>-fibre axis at 700 °C, a new, but weak <100> texture has developed parallel to the shortening axis. The Degtiarka pyrite (PN-6) initially has two weak fibre components. The somewhat stronger component is a <100>-fibre texture, similar to that in the experimentally deformed B-1 pyrite. The other one is a <111>-fibre texture similar to the intital B-1 preferred orientation. After 30% shortening oblique to both initial fibre axes at 600 °C, weak <110>- and <111>-fibre textures have developed. The experimentally produced fabrics have developed during deformation involving dislocation flow, dynamic recrystallisation and some microcracking. Intergranular sliding may also have been involved. Differences between lattice preferred orientations developed in the 600 °C and 700°C experiments are interpreted to indicate a change in the dominant flow mechanism with changing temperature.

In comparison with other cubic minerals that have been deformed experimentally by dislocation flow mechanisms, the pyrite shows an unusually weak preferred orientation which can be detected only by means of neutron diffraction texture goniometry.

Keywords: pyrite • experimental deformation • neutron texture goniometry • preferred orientation • orientation distribution function

Mineralogical Magazine; March 1993 v. 57; no. 386; p. 29-43; DOI: 10.1180/minmag.1993.057.386.04
© 1993, The Mineralogical Society
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