Abstract
Specimens of hornblende single crystals, deformed by Rooney et al. (1973, 1974), have been investigated by Tem. The main deformation features appear to be (101) twins, frequently containing high densities of dislocations. The major slip system appears to be (100) [001], with minor contributions from (010) [001], (010) [100], and (001) [100] also being possible. The strain contributed by the latter dislocations appears, however, to constitute only a small fraction of the strain accommodated by each specimen. A possible mechanism for the twinning process is constructed by considering the available observations in terms of details of the crystal structure. In addition the abundance of the various deformation mechanisms is discussed on the basis of crystallographic constraints.
A significant amount of sub-microscopic exsolution is observed in all specimens, frequently as small (100) and (101) lamellae, while in deformed regions a form of exsolution consisting of (100) platelets aligned along dislocations is observed. This mode of exsolution is considered to have occurred during the experiments, and a mechanism is proposed which involves preferential nucleation of the second phase in the local stress field of the dislocations.
