Azteccrystal

The eggshell fragments were embedded in epoxy resin and processed in steps according to the EBSD requirement. First, each specimen was grinded sequentially by abrasive paper with seven different grain sizes and polished through 3 different sizes of alumina suspension by grinder-polisher (MetaServ 250, Buehler Ltd., Lake Bluff, Illinois, USA). The specimens were then coated with platinum for better conductivity. Next, the EBSD maps were obtained using the symmetry detector attached to the field emission scanning electron microscope (JeoL JSM-7800F Prime, JEOL Ltd., Tokyo, Japan) with the following setting: accelerating voltage 20.0 kV; 70 degrees tilting of specimens. According to previous studies, the crystal lattice of Testudines eggshells was set to aragonite [21 (link),22 ], and the crystal lattice of gecko and crocodile eggshells was calcite [8 (link),23 (link)]. Finally, the grain sizes of eggshell data were analyzed by the software AZtecCrystal (Oxford Instruments, Oxfordshire, UK). The species of EBSD samples were the same as those used in SEM.

We examined outcrop‐scale structures within serpentinite exposed at Mie, near Nagasaki, Japan (Figure 1a). Polished thin sections for microstructural analysis were prepared in the x‐z plane of the finite strain ellipsoid. Electron images were produced using a Zeiss Sigma Field Emission Gun Scanning Electron Microscope (FEG‐SEM) at the School of Earth and Environmental Sciences, Cardiff University. EBSD data were collected using an Oxford Instruments Symmetry EBSD detector in an FEI Quanta FEG‐SEM at the School of Earth and Environment, University of Leeds. EBSD patterns were collected at a step size 0.1 μm using a 20 kV electron beam. The Oxford Instruments program AZtec Crystal and the mtex toolbox for matlab (Bachmann et al., 2010 (link)) were used to process the data. A description of the processing routine is provided with the EBSD data. Raman spectra were collected using a WITec Alpha 300R + confocal Raman microscope in the Department of Chemistry, University of Otago, New Zealand. Analytical and data processing methods followed those described in Rooney et al. (2018 (link)).

To reveal the microstructure of the material, electrolytic etching was performed (oxalic acid 10%, 3 V, 50 s), and then the grain sizes were measured following the ASTM standard E112-13, using the line-intercept method. Before the electron backscattered diffraction (EBSD) measurements, the material was polished using vibration polishing while being immersed in colloidal silica (0.04 µm) for 5 h. The scanning electron microscope (SEM) used was a Gemini 450 (ZEISS), equipped with an EBSD detector. The detector used was a Symmetry detector from Oxford Instruments. The acceleration voltage was set to 15 kV with a current of 1.2 nA. For the inverse-pole-figure (IPF) maps, a step size of 2 µm was utilized. Post-processing of the images was performed using Oxford Instruments software Aztec Crystal, where 5 neighboring grains were used to determine the unindexed pixels. This software was also utilized to obtain the preferred crystallographic direction in the material (i.e., multiples of random distribution (MRD) values). The IPF maps were also used for verifying the grain size measurements obtained using optical microscopy. All the fracture surfaces were investigated and the fractography was performed using an EVO 50 SEM (ZEISS).