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Title: Spherulitic Growth of Coral Skeletons and Synthetic Aragonite: Nature’s Three-Dimensional Printing

Abstract

Coral skeletons were long assumed to have a spherulitic structure, that is, a radial distribution of acicular aragonite (CaCO 3) crystals with their c-axes radiating from series of points, termed centers of calcification (CoCs). This assumption was based on morphology alone, not on crystallography. In this paper, we measure the orientation of crystals and nanocrystals and confirm that corals grow their skeletons in bundles of aragonite crystals, with their c-axes and long axes oriented radially and at an angle from the CoCs, thus precisely as expected for feather-like or “plumose” spherulites. Furthermore, we find that in both synthetic and coral aragonite spherulites at the nanoscale adjacent crystals have similar but not identical orientations, thus demonstrating by direct observation that even at nanoscale the mechanism of spherulite formation is non-crystallographic branching (NCB), as predicted by theory. Finally, synthetic aragonite spherulites and coral skeletons have similar angle spreads, and angular distances of adjacent crystals, further confirming that coral skeletons are spherulites. This is important because aragonite grows anisotropically, 10 times faster along the c-axis than along the a-axis direction, and spherulites fill space with crystals growing almost exclusively along the c-axis, thus they can fill space faster than any other aragonite growthmore » geometry, and create isotropic materials from anisotropic crystals. Greater space filling rate and isotropic mechanical behavior are key to the skeleton’s supporting function and therefore to its evolutionary success. Finally, in this sense, spherulitic growth is Nature’s 3D printing.« less

Authors:
 [1];  [2];  [1];  [1];  [3]; ORCiD logo [1]
  1. Univ. of Wisconsin, Madison, WI (United States)
  2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  3. Univ. of Haifa (Israel)
Publication Date:
Research Org.:
Univ. of Wisconsin, Madison, WI (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Univ. of Haifa (Israel)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF); Israel Science Foundation; United States–Israel Binational Science Foundation (BSF)
OSTI Identifier:
1379910
Grant/Contract Number:
AC02-05CH11231; FG02-07ER15899; DMR-1603192; 312/15; BSF-2010065; BSF-2014035
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
ACS Nano
Additional Journal Information:
Journal Volume: 11; Journal Issue: 7; Journal ID: ISSN 1936-0851
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 36 MATERIALS SCIENCE; biomineralization; CPA; crystallization by particle attachment; ion attachment; mesocrystal; PEEM; PIC-mapping

Citation Formats

Sun, Chang-Yu, Marcus, Matthew A., Frazier, Matthew J., Giuffre, Anthony J., Mass, Tali, and Gilbert, Pupa U. P. A. Spherulitic Growth of Coral Skeletons and Synthetic Aragonite: Nature’s Three-Dimensional Printing. United States: N. p., 2017. Web. doi:10.1021/acsnano.7b00127.
Sun, Chang-Yu, Marcus, Matthew A., Frazier, Matthew J., Giuffre, Anthony J., Mass, Tali, & Gilbert, Pupa U. P. A. Spherulitic Growth of Coral Skeletons and Synthetic Aragonite: Nature’s Three-Dimensional Printing. United States. doi:10.1021/acsnano.7b00127.
Sun, Chang-Yu, Marcus, Matthew A., Frazier, Matthew J., Giuffre, Anthony J., Mass, Tali, and Gilbert, Pupa U. P. A. 2017. "Spherulitic Growth of Coral Skeletons and Synthetic Aragonite: Nature’s Three-Dimensional Printing". United States. doi:10.1021/acsnano.7b00127.
@article{osti_1379910,
title = {Spherulitic Growth of Coral Skeletons and Synthetic Aragonite: Nature’s Three-Dimensional Printing},
author = {Sun, Chang-Yu and Marcus, Matthew A. and Frazier, Matthew J. and Giuffre, Anthony J. and Mass, Tali and Gilbert, Pupa U. P. A.},
abstractNote = {Coral skeletons were long assumed to have a spherulitic structure, that is, a radial distribution of acicular aragonite (CaCO3) crystals with their c-axes radiating from series of points, termed centers of calcification (CoCs). This assumption was based on morphology alone, not on crystallography. In this paper, we measure the orientation of crystals and nanocrystals and confirm that corals grow their skeletons in bundles of aragonite crystals, with their c-axes and long axes oriented radially and at an angle from the CoCs, thus precisely as expected for feather-like or “plumose” spherulites. Furthermore, we find that in both synthetic and coral aragonite spherulites at the nanoscale adjacent crystals have similar but not identical orientations, thus demonstrating by direct observation that even at nanoscale the mechanism of spherulite formation is non-crystallographic branching (NCB), as predicted by theory. Finally, synthetic aragonite spherulites and coral skeletons have similar angle spreads, and angular distances of adjacent crystals, further confirming that coral skeletons are spherulites. This is important because aragonite grows anisotropically, 10 times faster along the c-axis than along the a-axis direction, and spherulites fill space with crystals growing almost exclusively along the c-axis, thus they can fill space faster than any other aragonite growth geometry, and create isotropic materials from anisotropic crystals. Greater space filling rate and isotropic mechanical behavior are key to the skeleton’s supporting function and therefore to its evolutionary success. Finally, in this sense, spherulitic growth is Nature’s 3D printing.},
doi = {10.1021/acsnano.7b00127},
journal = {ACS Nano},
number = 7,
volume = 11,
place = {United States},
year = 2017,
month = 5
}

Journal Article:
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  • Coral skeletons are constructed of aragonitic crystals organized into fan systems. A theoretical model for the growth of such fan systems, which depends upon competition between crystals for space in which to grow, is corroborated by vital staining with sodium alizarinesulfonate. Fan systems of crystals compete with each other to form larger fan systems until large, relatively stable fans are produced. It is these relatively stable fan systems that have been observed in optical thin sections of coral skeletons. (13 refs.)
  • Magnetic fields are an essential component of a plasma. In many astrophysical, solar, magnetospheric, and laboratory situations the magnetic field in the plasma can be very dynamic and form highly complex structures. One approach to unraveling these structures is to determine the magnetic skeleton of the field, a set of topological features that divide the magnetic field into topologically distinct domains. In general, the features of the magnetic skeleton are difficult to locate, in particular those given by numerical experiments. In this paper, we propose a new set of tools to find the skeleton of general magnetic fields including nullmore » points, spines, separatrix surfaces, and separators. This set of tools is found to be considerably better at finding the skeleton than the currently favored methods used in magnetohydrodynamics.« less
  • The strontium to calcium ratio of skeletal aragonite in three genera of reef-building corals varies as a sinple function of temperature and the strontium to calcium ratio of the incubation water. The strontium/calcium distribution coefficients of coral aragonite apparently differ from the corresponding coefficient of inorganically precipitated aragonite. With some care, coral skeletons can be used as recording thermometers.
  • A comparative study of Pleistocene fossil coral skeletons and of modern coral skeletons was carried out using petrographic and trace element analyses on a suite of Pleistocene samples that had previously been studied from [sup 234]U, [sup 230]Th, and U-[sup 230]Th ages (Chen et al. 1991). Evidence of a range of diagenetic changes can be recognized by optical (OM) and scanning electron microscopy (SEM). Using an electron microprobe and SEM, concentrations of Na, S, Sr, and Mg were measured. No other trace elements were detected. Na, S, and Mg contents of the matrix, the fibrous micropores, and radiating needles aremore » highly variable and well correlated. High concentrations of Na, S, and Mg were found in modern living corals with lower concentrations in fossil corals and fibrous micropores, and the lowest value in the radiating needles. The reason for the correlations of Na, S, and Mg and crystal chemistry and the response to diagenesis of these trace elements is not understood. The average concentrations of Na, S, and Mg for each sample, when plotted against the whole coral initial [delta][sup 234]U, are generally correlated (Chen et al., 1991). As all these diagenetic changes involve the recystallization and deposition of aragonite, the authors infer that the geologic site of diagenesis both for forming the secondary aragonitic phases and for the enhancement of the [sup 234]U content in the fossil corals was the marine environment. It is possible that the textural and Na, S, and Mg trace element contents of fossil corals be used to ascertain the reliability of fossil coral skeletons for U-[sup 230]Th dating. The basic problem of identifying a priori unaltered coral skeletons for [sup 230]Th dating is not yet resolved. 64 refs., 16 figs., 5 tabs.« less