11 research outputs found
Nacre tablet thickness records formation temperature in modern and fossil shells
Nacre, the iridescent outer lining of pearls and inner lining of many mollusk shells, is composed of periodic, parallel, organic sheets alternating with aragonite (CaCO_3) tablet layers. Nacre tablet thickness (TT) generates both nacre's iridescence and its remarkable resistance to fracture. Despite extensive studies on how nacre forms, the mechanisms controlling TT remain unknown, even though they determine the most conspicuous of nacre's characteristics, visible even to the naked eye.
Thermodynamics predicts that temperature (T) will affect both physical and chemical components of biomineralized skeletons. The chemical composition of biominerals is well-established to record environmental parameters, and has therefore been extensively used in paleoclimate studies. The physical structure, however, has been hypothesized but never directly demonstrated to depend on the environment. Here we observe that the physical TT in nacre from modern and fossil shallow-water shells of the bivalves Pinna and Atrina correlates with T as measured by the carbonate clumped isotope thermometer. Based on the observed TT vs. T correlation, we anticipate that TT will be used as a paleothermometer, useful to estimate paleotemperature in shallow-water paleoenvironments. Here we successfully test the proposed new nacre TT thermometer on two Jurassic Pinna shells. The increase of TT with T is consistent with greater aragonite growth rate at higher T, and with greater metabolic rate at higher T. Thus, it reveals a complex, T-dependent biophysical mechanism for nacre formation
Mollusk Shell Nacre Ultrastructure Correlates with Environmental Temperature and Pressure
Nacre, or mother-of-pearl, the tough, iridescent biomineral
lining
the inner side of some mollusk shells, has alternating biogenic aragonite
(calcium carbonate, CaCO<sub>3</sub>) tablet layers and organic sheets.
Nacre has been common in the shells of mollusks since the Ordovician
(450 million years ago) and is abundant and well-preserved in the
fossil record, e.g., in ammonites. Therefore, if any measurable physical
aspect of the nacre structure was correlated with environmental temperatures,
one could obtain a structural paleothermometer of ancient climates.
Using X-ray absorption near-edge structure (XANES) spectroscopy, Photoelectron
emission spectromicroscopy (PEEM), and X-ray linear dichroism we acquired
polarization-dependent imaging contrast (PIC) maps of pristine nacre
in cross-section. The new PIC-map data reveal that the nacre ultrastructure
(nacre tablet width, thickness, and angle spread) is species-specific
in at least eight mollusk species from completely different environments: <i>Nautilus pompilius</i>, <i>Haliotis iris</i>, <i>Haliotis rufescens</i>, <i>Bathymodiolus azoricus</i>, <i>Atrina rigida</i>, <i>Lasmigona complanata</i>, <i>Pinctada margaritifera</i>, and <i>Mytilus californianus</i>. Nacre species-specificity is interpreted as a result of adaptation
to diverging environments. We found strong correlation between nacre
crystal misorientations and environmental temperature, further supported
by secondary ion mass spectrometry measurements of <i>in situ</i> δ<sup>18</sup>O in the nacre of one shell. This has far-reaching
implications: nacre texture may be used as a paleothermometer of ancient
climate, spanning 450 million years of Earth's history
Mollusk Shell Nacre Ultrastructure Correlates with Environmental Temperature and Pressure
Nacre, or mother-of-pearl, the tough, iridescent biomineral
lining
the inner side of some mollusk shells, has alternating biogenic aragonite
(calcium carbonate, CaCO<sub>3</sub>) tablet layers and organic sheets.
Nacre has been common in the shells of mollusks since the Ordovician
(450 million years ago) and is abundant and well-preserved in the
fossil record, e.g., in ammonites. Therefore, if any measurable physical
aspect of the nacre structure was correlated with environmental temperatures,
one could obtain a structural paleothermometer of ancient climates.
Using X-ray absorption near-edge structure (XANES) spectroscopy, Photoelectron
emission spectromicroscopy (PEEM), and X-ray linear dichroism we acquired
polarization-dependent imaging contrast (PIC) maps of pristine nacre
in cross-section. The new PIC-map data reveal that the nacre ultrastructure
(nacre tablet width, thickness, and angle spread) is species-specific
in at least eight mollusk species from completely different environments: <i>Nautilus pompilius</i>, <i>Haliotis iris</i>, <i>Haliotis rufescens</i>, <i>Bathymodiolus azoricus</i>, <i>Atrina rigida</i>, <i>Lasmigona complanata</i>, <i>Pinctada margaritifera</i>, and <i>Mytilus californianus</i>. Nacre species-specificity is interpreted as a result of adaptation
to diverging environments. We found strong correlation between nacre
crystal misorientations and environmental temperature, further supported
by secondary ion mass spectrometry measurements of <i>in situ</i> δ<sup>18</sup>O in the nacre of one shell. This has far-reaching
implications: nacre texture may be used as a paleothermometer of ancient
climate, spanning 450 million years of Earth's history
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Parrotfish Teeth: Stiff Biominerals Whose Microstructure Makes Them Tough and Abrasion-Resistant To Bite Stony Corals
Parrotfish (<i>Scaridae</i>) 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 <i>Chlorurus microrhinos</i> tooth. Its enameloid is a fluorapatite
(Ca<sub>5</sub>(PO<sub>4</sub>)<sub>3</sub>F) 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<sup>1/2</sup>, 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
Amorphous calcium carbonate particles form coral skeletons
Do corals form their skeletons by precipitation from solution or by attachment of amorphous precursor particles as observed in other minerals and biominerals? The classical model assumes precipitation in contrast with observed "vital effects," that is, deviations from elemental and isotopic compositions at thermodynamic equilibrium. Here, we show direct spectromicroscopy evidence in Stylophora pistillata corals that two amorphous precursors exist, one hydrated and one anhydrous amorphous calcium carbonate (ACC); that these are formed in the tissue as 400-nm particles; and that they attach to the surface of coral skeletons, remain amorphous for hours, and finally, crystallize into aragonite (CaCO3). We show in both coral and synthetic aragonite spherulites that crystal growth by attachment of ACC particles is more than 100 times faster than ion-by-ion growth from solution. Fast growth provides a distinct physiological advantage to corals in the rigors of the reef, a crowded and fiercely competitive ecosystem. Corals are affected by warming-induced bleaching and postmortem dissolution, but the finding here that ACC particles are formed inside tissue may make coral skeleton formation less susceptible to ocean acidification than previously assumed. If this is how other corals form their skeletons, perhaps this is how a few corals survived past CO2 increases, such as the Paleocene-Eocene Thermal Maximum that occurred 56 Mya
Oxygen spectroscopy and polarization-dependent imaging contrast (PIC)-mapping of calcium carbonate minerals and biominerals
X-ray absorption near-edge structure (XANES) spectroscopy and spectromicroscopy have been extensively used to characterize biominerals. Using either Ca or C spectra, unique information has been obtained regarding amorphous biominerals and nanocrystal orientations. Building on these results, we demonstrate that recording XANES spectra of calcium carbonate at the oxygen K-edge enables polarization-dependent imaging contrast (PIC) mapping with unprecedented contrast, signal-to-noise ratio, and magnification. O and Ca spectra are presented for six calcium carbonate minerals: aragonite, calcite, vaterite, monohydrocalcite, and both hydrated and anhydrous amorphous calcium carbonate. The crystalline minerals reveal excellent agreement of the extent and direction of polarization dependences in simulated and experimental XANES spectra due to X-ray linear dichroism. This effect is particularly strong for aragonite, calcite, and vaterite. In natural biominerals, oxygen PIC-mapping generated high-magnification maps of unprecedented clarity from nacre and prismatic structures and their interface in Mytilus californianus shells. These maps revealed blocky aragonite crystals at the nacre-prismatic boundary and the narrowest calcite needle-prisms. In the tunic spicules of Herdmania momus, O PIC-mapping revealed the size and arrangement of some of the largest vaterite single crystals known. O spectroscopy therefore enables the simultaneous measurement of chemical and orientational information in CaCO3 biominerals and is thus a powerful means for analyzing these and other complex materials. As described here, PIC-mapping and spectroscopy at the O K-edge are methods for gathering valuable data that can be carried out using spectromicroscopy beamlines at most synchrotrons without the expense of additional equipment
Oxygen Spectroscopy and Polarization-Dependent Imaging Contrast (PIC)-Mapping of Calcium Carbonate Minerals and Biominerals
X-ray
absorption near-edge structure (XANES) spectroscopy and spectromicroscopy
have been extensively used to characterize biominerals. Using either
Ca or C spectra, unique information has been obtained regarding amorphous
biominerals and nanocrystal orientations. Building on these results,
we demonstrate that recording XANES spectra of calcium carbonate at
the oxygen K-edge enables polarization-dependent imaging contrast
(PIC) mapping with unprecedented contrast, signal-to-noise ratio,
and magnification. O and Ca spectra are presented for six calcium
carbonate minerals: aragonite, calcite, vaterite, monohydrocalcite,
and both hydrated and anhydrous amorphous calcium carbonate. The crystalline
minerals reveal excellent agreement of the extent and direction of
polarization dependences in simulated and experimental XANES spectra due to X-ray linear dichroism. This effect is particularly strong
for aragonite, calcite, and vaterite. In natural biominerals, oxygen
PIC-mapping generated high-magnification maps of unprecedented clarity from nacre and prismatic
structures and their interface in Mytilus californianus shells. These maps revealed blocky aragonite
crystals at the nacre–prismatic boundary and the narrowest
calcite needle-prisms. In the tunic spicules of Herdmania
momus, O PIC-mapping revealed the size and arrangement
of some of the largest vaterite single crystals known. O spectroscopy
therefore enables the simultaneous measurement of chemical and orientational
information in CaCO<sub>3</sub> biominerals and is thus a powerful
means for analyzing these and other complex materials. As described
here, PIC-mapping and spectroscopy at the O K-edge are methods for
gathering valuable data that can be carried out using spectromicroscopy
beamlines at most synchrotrons without the expense of additional equipment