Dislocation-Dissociations and the SFE in Magnesium Aluminate Spinel

High-temperature creep deformation of synthetic forsterite crystals, as studied by Darot and Gueguen [162], occurred by (010) [100] sUp, which is apparently the preferred slip system. This same slip system was detected around Vickers indents produced at temperatures of 600 °C and above by Gaboriaud et al. (163, 164], who used natural olivine single crystals from San Carlos, Arizona (110) [001] slip was also activated. There have been many other extensive deformation studies of the olivine minerals (e.g., see Kohlstedt and Ricoult [165] and Poumellec and Jaoul [166]). 

Dislocation-dissociation has also been an issue in olivine since the early studies of Poirier et al. [161,172]. Evidence for such dissociation, usingTEM, was first reported by Van der Sande and Kohlstedt [173], and more recently by Smith et al. [174] and Drury [34]. The dissociation [Eqs (18) and (19)] suggested by Poirier assumes that the oxygen ions can be considered as hard spheres  

Hydration-induced climb dissociation of dislocations in naturally deformed mantle olivine has been reported by Drury [171]. Here, the dissociation is pro- 

2) The official space group in the International Tkbles of X-ray crystallography is Pnma (no. 62), but the historical axes given above mean that the space group permutes to Pbnm. 

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