Development of microstructure during deformation of carnallite and bischofite in transmitted light

Abstract

During deformation of 5 × 5 × 0.1 mm samples of carnallite and bischofite in transmitted light, the development of the microstructure was followed by time-lapse photography. In dry samples, carnallite deforms by mechanical twinning, intracrystalline slip and by cataclastic processes. The addition of brine strongly enhances dynamic recrystallization by progressive misorientation of subgrains and by grain boundary migration. Bischofite shows similar behaviour, in agreement with results from samples deformed in a triaxial apparatus. Important microstructural processes during dynamic recrystallization of wet bischofite are grain coalescence, grain dissection and grain migration. The oscillatory motion of grain boundaries and sudden large changes in grain boundary migration rate were important features.