Electron Microscopy. After the PLM experiment, we used the same thin section of the sample for the SEM
experiment. In order to lower surface charging of the sample, it was sputtered with carbon prior to the SEM
experiment. We used a JEOL-JSM-6060LV scanning electron microscope from Jeol, Eching, Germany with an
acceleration voltage of 10 kV. Several images of each grain were collected with a back-scattered electron detector at
different magnification factors reaching from 15 up to 2000. The SEM images of Fig. 4 in the main text and Fig. S1
of the supplementary information were acquired with a magnification of 2000 while the SEM images in Fig. S2 of
the supplementary information show the grains with a magnification of 200.