We study how crystals are oriented in tooth enamel, including human, mouse, parrotfish, and many other animals. PIC mapping, based on x-ray linear dichroism of apatite, reveals nano- and micro-scale arrangement of crystals and displays them in color. Molecular dynamics simulations by Markus Buehler and his group confirm that the small misorientations observed in human enamel deflect fractures and that human enamel self-heals after fracturing. See papers 147, 150, 154, 157. These are Marcus et al. ACS Nano 2017, Stifler et al. J Am Chem Soc 2018, Beniash et al. Nat Comms 2019, Stifler et al. Acta Biomaterialia 2021, and others submitted.