Deformation of dolomite single crystals from 20?800� C

Abstract

Dolomite single crystals of six different crystallographic orientations were tested in compression under confining pressure at temperatures of 20 to 800° C. The chosen orientations favoured slip or twinning on particular systems. The deformed crystals were analysed by optical and high voltage transmission electron microscopy to determine activated deformation systems, dislocation behaviour, etc., and to assist in interpreting stress-strain data. It is shown that slip on c≡(0001) and on $$f \equiv (\bar 1012)$$ ), and twinning on f between 300 and 600° C, are the principal modes of deformation. At low temperatures there is considerable cataclasis, and shear-fracturing must be counted as a significant deformation mechanism. The effects of climb become apparent at temperatures ≳600° C. A pronounced increase in strength with testing temperature shown by some orientations of the crystals is largely associated with c slip, but f twinning also shows similar although weaker tendencies. The yield stress for f slip decreases markedly with temperature. Values of critical resolved shear stress are obtained for c and f slip, and for f twinning. Major and minor slip systems, dislocation and twin configurations generated by deformation under different regimes are documented and illustrated. Some of the characteristics of the deformation systems are attributed to the details of atomic displacements. In particular, the increase in strength with temperature for c slip is explained by friction of CO 3 2− groups during dislocation movement, which is unique for c slip. This friction increases with thermal vibration, expansion and rotation of the CO 3 2− groups.