CET/UWA Microstructure CourseCET/UWA Microstructure Course| NAME OF PROCESS(P) OR MECHANISM (M) | ATOMIC SCALE PROCESS | DIAGNOSTIC MICRO-
STRUCTURES |
Grain Shape Foliation | Crystallographic Preferred Orientation | RHEOLOGICAL IMPLICATIONS | COMMON MINERALS |
| Fracturing (M) | Breaking of inter-atomic bonds | Gouge, breccias, boudinaged grains | +ve or -ve | -ve (ie negative, is weakened by this mechanism) | Any, more at high stress & low T | |
| Frictional Sliding (M) | Frictional sliding on surfaces | Gouges, breccias, pseudotachylites, domino grains | +ve or -ve | -ve |  |
Any, more at high stress & low T |
| Diffusional Creep (M) | Diffusional movement of vacancies and interstitials | New crystal void of pre-existing impurities (hard to prove in nature) | +ve | ? | 
(Nabarro-Herring) or  (Coble
creep) |
Any, more at low stress & high T |
| Dislocation Glide (M) | Re-arrangement of inter-atomic bonds | Deformation lamellae, deformation bands, undulose extinction | +ve | ++ve | 
also a hardening with finer grain size (Hall-Petch Law) |
Any, more at low stress & high T |
| Twinning (M) | Re-arrangement of inter-atomic bonds and re-orientation of lattice site | Twins (sharp nosed, narrow, parallel to rational twin planes) | +ve | +ve | Calcite especially at low T and low strain, plagioclase, quartz (but not visible), amphiboles | |
| Kinking (M) | Dislocation glide on single slip system | Kink bands | +ve | +ve | Micas, low T quartz, kyanite | |
| Grain Boundary Migration (P or M) | Atomic scale diffusional processes, possibly involving dissolution and precipitation | Irregular grain boundaries, pinning microstructures, orientation families, Lattice preferred orientations with strong point maxima, non-120°-triple junctions | +ve or -ve | +ve | Produces low dislocation density material Q softer | Any, more at high T, especially quartz, olivine, fsp |
| Rotation Recrystallisation (P) | Progressive addition of dislocations of same sign to sub-grain wall | Mortar texture or core and mantle texture, bi-modal grain size | -ve | -ve | Change in grain size can strengthen or weaken material | Any, more at low stress & high T, especially quartz, fsp, olivine |
| Recovery (P) | Climb, mutual annihilation of dislocations of opposite signs, formation of subgrain walls | Polygonisation, foam textures, 120°-triple junctions | -ve | +ve or -ve | Produces low dislocation density material Q softer | Any, more at high T |
| Climb (M) | Diffusional addition or removal of atoms at dislocation line | +ve | 0 | Any, more at high T | ||
| Lattice Rotation (P) | Dislocation glide and/or bulk rotation of grains | Crystallographic preferred orientations | 0 | +ve | Well developed fabrics may be stronger or weaker than random fabrics | Any, more at low stress & high T |
| Bulk Rotation (M or P) | Physical rotation of whole or part of mineral grains | Helical inclusion trails, bending of crystals, delta & sigma porphyroclasts | +ve | +ve or -ve | Any | |
| Grain Boundary Sliding (M) | Dislocation movement on "clean" grain boundaries, shearing on "dirty" ones | 0 | 0 | Any | ||
| Diffusive Mass Transfer (M or P) | "Long range" diffusion of atoms | Veins, pressure shadows, porhyroblasts | +ve or -ve | +ve | Any, especially quartz and calcite | |
| Phase Change (M or P) | Changed crystal structure without change in bulk chemistry of mins | Phase boundaries in minerals | ? | ? | Often associated with volume change | Quartz, calcite-aragonite, olivine |