Parrotfish (Scaridae) feed by biting stony corals. To investigate how their teeth endure the associated contact stresses, we examine the chemical composition, nano- and microscale structure, and the mechanical properties of the steephead parrotfish Chlorurus microrhinos tooth. Its enameloid is a fluorapatite (Ca₅(PO₄)₃F) biomineral with outstanding mechanical characteristics: the mean elastic modulus is 124 GPa, and the mean hardness near the biting surface is 7.3 GPa, making this one of the stiffest and hardest biominerals measured; the mean indentation yield strength is above 6 GPa, and the mean fracture toughness is ∼2.5 MPa·m^1/2, relatively high for a highly mineralized material. This combination of properties results in high abrasion resistance. Fluorapatite X-ray absorption spectroscopy exhibits linear dichroism at the Ca L-edge, an effect that makes peak intensities vary with crystal orientation, under linearly polarized X-ray illumination. This observation enables polarization-dependent imaging contrast mapping of apatite, a method to quantitatively measure and display nanocrystal orientations in large, pristine arrays of nano- and microcrystalline structures. Parrotfish enameloid consists of 100 nm-wide, microns long crystals co-oriented and assembled into bundles interwoven as the warp and the weave in fabric and therefore termed fibers here. These fibers gradually decrease in average diameter from 5 μm at the back to 2 μm at the tip of the tooth. Intriguingly, this size decrease is spatially correlated with an increase in hardness.

中文翻译：

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鹦嘴鱼牙齿：坚硬的生物矿物，其微观结构使它们坚韧耐磨，能耐石质珊瑚咬伤

鹦嘴鱼（Scaridae）以咬石珊瑚为食。为了研究它们的牙齿如何承受相关的接触应力，我们检查了steep头鹦嘴鱼Chlorurus microrhinos牙齿的化学成分，纳米和微米级结构以及机械性能。它的同种生物是具有出色机械特性的氟磷灰石（Ca ₅（PO ₄）₃ F）生物矿物：平均弹性模量为124 GPa，咬合表面附近的平均硬度为7.3 GPa，使其成为最坚硬的生物矿物之一测量 平均压痕屈服强度大于6 GPa，平均断裂韧性为〜2.5 MPa·m ^1/2，对于高度矿化的材料来说相对较高。这些特性的结合导致了高耐磨性。氟磷灰石X射线吸收光谱法在Ca L边缘显示线性二向色性，这种作用使峰强度在线性偏振X射线照明下随晶体取向而变化。该观察结果使磷灰石的偏振相关成像对比度映射成为可能，这是一种定量测量和显示大型原始阵列中纳米和微晶结构的纳米晶取向的方法。鹦嘴鱼同名生物由共取向的100纳米宽，微米长的晶体组成，并组装成在织物中经纱和编织时交织在一起的束，因此在此称为纤维。这些纤维的平均直径从背面的5μm逐渐减小到齿尖的2μm。有趣的是