Deformation twinning in calcite,dolomite, and other rhombohedral carbonates |
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| Authors: | D J Barber H -R Wenk |
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| Institution: | 1. Physics Department, University of Essex, Colchester, Essex, England
2. Department of Geology and Geophysics, University of California, 94720, Berkeley, California, U.S.A.
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| Abstract: | Transmission electron microscope (tem) observations of single and multiple twins in calcite and dolomite are presented, and the results are analysed by means of selected area diffraction and trace analysis. Simple twinning in rhodochrosite and kutnahorite is also analysed. It is shown that the ordered carbonates, such as dolomite, have a common twinning plane {01 \(\bar 1\) 2} and this appears to be their only mode of deformation twinning. The carbonates with higher symmetry, such as calcite, have {01 \(\bar 1\) 8} as the primary twinning plane but calcite itself has other twinning mechanisms, of which the most important is illustrated. Crossing and stopping twins are also discussed. It is shown that twinning in calcite, which occurs predominantly at low temperatures, is characterized by the generation of large numbers of glide dislocations. |
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