Coarsening in Coral Skeletons Formation

ORAL

Abstract

Spherulites in coral skeletons are composed of acicular aragonite crystals radiating from common centers and exhibiting a 0–35° misorientation of crystallographic c-axes across grain boundaries, previously misattributed entirely to a mechanism called non-crystallographic branching [1,2]. Here, we examine skeletons from 9 diverse species with quantitative nanoscale crystal orientation analyses using Polarization-dependent Imaging Contrast (PIC) mapping [3]. We discovered that, in addition to spherulites, 4 of the species also form tiny (0.2–2 µm), randomly oriented, equant crystals, termed sprinkles. Supported by theoretical phase field simulations, we propose that all initially nucleated crystals are randomly oriented sprinkles, and that these later coarsen, with radially oriented crystals growing at the expense of smaller, randomly oriented sprinkles. This mechanism is analogous to solidification or annealing in metals, both of which are high-temperature phenomena, whereas in coral skeletons coarsening occurs at ambient conditions.

1. Sun 2017, DOI: 10.1021/acsnano.7b00127
2. Gránásy 2005, DOI: 10.1103/PhysRevE.72.011605
3. Gilbert 2017, DOI: 10.1016/j.epsl.2016.11.012

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Presenters

  • Chang-Yu Sun

    Department of Physics, University of Wisconsin - Madison, University of Wisconsin - Madison

Authors

  • Chang-Yu Sun

    Department of Physics, University of Wisconsin - Madison, University of Wisconsin - Madison

  • László Gránásy

    Institute for Solid State Physics and Optics, Wigner Research Centre for Physics

  • Cayla Stifler

    Department of Physics, University of Wisconsin - Madison, University of Wisconsin - Madison

  • Jun A. Y. Zhang

    Department of Physics, University of Wisconsin - Madison

  • Tal Zaquin

    Marine Biology Department, University of Haifa

  • Tali Mass

    Marine Biology Department, University of Haifa

  • Stefano Goffredo

    Marine Science Group, Department of Biological, Geological and Environmental Sciences, University of Bologna

  • Giuseppe Falini

    Department of Chemistry “Giacomo Ciamician”, Alma Mater Studiorum – University of Bologna

  • James C Weaver

    Wyss Institute for Biologically Inspired Engineering, Harvard University, Wyss Institute, Harvard University

  • Matthew a Marcus

    Advanced Light Source, Lawrence Berkeley National Laboratory

  • Tamás Pusztai

    Institute for Solid State Physics and Optics, Wigner Research Centre for Physics

  • Pupa Gilbert

    University of Wisconsin, Madison, University of Wisconsin - Madison, Department of Physics, University of Wisconsin - Madison