Hematite Exsolutions in Corundum from Cenozoic Basalts in Changle, Shandong Province, China: Crystallographic Orientation Relationships and Interface Characters

Here, we present well-oriented hematite exsolutions in corundum megacrysts from Cenozoic basalt in China. Crystallographic orientation relationships (CORs) and the interface characters between the hematite exsolutions and the corundum host were analyzed by electron backscatter diffraction (EBSD) and high-resolution transmission electron microscope (HRTEM), respectively. The CORs and the regular interface confirm the exsolution and the exsolution was formed under depressurization based on the crystal chemistry theory. There are three groups of exsolutions intersected with ~60°. Two groups of the exsolutions have the same orientation with the host and the other group is twinned to those two groups. Focused ion beam (FIB) for HRTEM foil preparation was carried out. HRTEM photographs show that there are periodic coherency units at (0001) interface. The measured unit lengths are 6.71–6.72 nm, which are in good agreement with every 17-DCrn011¯2projection or 16-DHem011¯2projection. Based on the results, the possibility is that at the interface, the hematite-corundum phases tend to modulate to achieve the maximum coherency in the geological process during exsolution. This research is helpful to understand the interface characters between the exsolution and host.