Forward Scatter Electron (FSE) images of corona segments corresponding to EBSD data sets (a) Py1, (b) Pr1b, and (c) Py2 showing the polycrystalline nature of the spinel layer, the presence of very fine grained equant spinel grains close to the initial corundum/basalt interface, and the different microstructures of the inner and outer spinel layer. Note the micrometer scale cusps and steps of the final spinel/corundum interface indicated by arrows. White line markers in (b) highlight the position of the initial interface between corundum and melt (dotted line), the inner corona (dash-dotted line) and the outer corona (dashed line). The black rectangle in (c) highlights a wedge-shaped, basalt filled gap in the spinel rim.