ALBERT

Description: 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 - fibre texture perpendicular to a grain-size layering. After 24% shortening perpendicular to the - fibre axis at 700°C a new, but weak 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 -fibre texture, similar to that in the experimentally deformed B-1 pyrite. The other one is a - fibre texture similar to the intital B-1 preferred orientation. After 30% shortening oblique to both initial fibre axes at 600°C weak - and -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.