Hollow grains exhibit no obvious preferred orientation with respect to the host IDP. (a) and (b) Volume-rendered image of hollow grains (arrows) viewed from two different angles. The nanohole of the grain (arrow in panel (a)) is hidden in panel (b), with its orientation considerably different from that of the grain (arrow in panel (b)), although the two are in the same cluster. (c) Volume-rendered image showing the hollow grain (arrow in Figure 1(b)) with the nanohole revealed by tilting forward and sideways relative to Figure 1(b). Volume: 0.8 × 1.0 × 1.0 μm³.