Modular aspects of the crystal structures of kurchatovite and clinokurchatovite

Experimental deformation of diopside single crystals has been carried out in the temperature range 800-900 degrees C at 750 MPa confining pressure at strain rates of 1.5-3 x10-5 s-1. Four compression orientations have been tested in order to study all the possible glide systems. TEM observations of the deformed samples show that the [001] (100) glide system is the easiest one with a critical resolved shear stress of the order of 60 MPa. Both glide systems [100] (010) and 1/2 {110} can also be activated but these require larger resolved shear stresses of the order of 200 MPa. [001] (010) has been observed in one of the samples, indicating that it is difficult to activate in the temperature range considered. There is no evidence of c glide in the {110} planes in contrast with omphacite. As our starting material contains small amounts of OH, we have annealed one of the crystals for 70 hours at 1050 degrees C in order to remove all the hydroxyls. No significant difference is observed between the mechanical behaviour of this "dry" sample and the "wet" material.