Scanning electron microscope (SEM) orientation contrast images of mantle nodules show that garnets contain cellular domains of different crystallographic orientation. Electron backscatter diffraction shows small crystallographic mismatches (<3°) across cell boundaries. A transmission electron microscope examination of an area containing these substructures shows that the cell boundaries comprise arrays of dislocations and are subgrain boundaries. The observed garnet substructures relate to high-temperature dislocation creep and recovery. This is the first time that subgrains have been shown to occur in a significant volume of an individual garnet. Wider application of new SEM techniques may enable us to use garnet microstructures to determine deformation conditions more exactly and will aid interpretation of garnet microchemical data.

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