Aragonite and Calcite Crystallography in Coral

The surface sample (of thick slides) was polished with alumina of 1 µm, 0.3 µm, and 0.05 µm and finally polished with colloidal silica (0.05 µm). Before analysis, samples were coated with a thin layer (ca. 2 nm) of carbon using a high vacuum coater. The EBSD study was carried out with Oxford NordlysMax detector mounted on a scanning electron microscope JEOL JSM-6610LV at the Institute of Materials Engineering, Łódź University of Technology. EBSD data were collected with AztecHKL software at high vacuum, 20 kV, large probe current, and 20 mm of working distance. EBSD patterns were collected at a resolution of 0.22 μm step size for crystallographic maps using the unit cell settings characteristic of aragonite and calcite as follows^{58 (link),59 (link)}: “Pmcn” symmetry and a = 4.96 Å, b = 7.97 Å, and c = 5.75 Å estimated for Favia coral using X-ray powder diffraction with synchrotron radiation (43) and a = b = 4.99 Å, and c = 17.06 Å, respectively. The EBSD data are represented in this study by crystallographic maps, phase images, and the pole figures, which represent the stereographic projection of crystallographic planes in reference to the (100), (010), (001) and (222) aragonite planes. Orientation images and the pole figures were created using MTEX open source plugin for Matlab program (https://mtex-toolbox.github.io/). To eliminate combination of red and green colors and create images more accessible for color-blind users we selected BungeColorKey palette from MTEX (the outcome was tested using Coblis, the Color Blindness Simulator at https://www.color-blindness.com/coblis-color-blindness-simulator/).