title: Oxygen spectroscopy and polarization-dependent imaging contrast (PIC)-mapping of calcium carbonate minerals and biominerals.
abstract: 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.
authors.affiliation: Department of Physics, University of Wisconsin-Madison , 1150 University Avenue, Madison, Wisconsin 53706, United States.
authors.forename: Ross T
authors.initials: RT
authors.lastname: DeVol
authors.forename: Rebecca A
authors.initials: RA
authors.lastname: Metzler
authors.forename: Lee
authors.initials: L
authors.lastname: Kabalah-Amitai
authors.forename: Boaz
authors.initials: B
authors.lastname: Pokroy
authors.forename: Yael
authors.initials: Y
authors.lastname: Politi
authors.forename: Assaf
authors.initials: A
authors.lastname: Gal
authors.forename: Lia
authors.initials: L
authors.lastname: Addadi
authors.forename: Steve
authors.initials: S
authors.lastname: Weiner
authors.forename: Alejandro
authors.initials: A
authors.lastname: Fernandez-Martinez
authors.forename: Raffaella
authors.initials: R
authors.lastname: Demichelis
authors.forename: Julian D
authors.initials: JD
authors.lastname: Gale
authors.forename: Johannes
authors.initials: J
authors.lastname: Ihli
authors.forename: Fiona C
authors.initials: FC
authors.lastname: Meldrum
authors.forename: Adam Z
authors.initials: AZ
authors.lastname: Blonsky
authors.forename: Christopher E
authors.initials: CE
authors.lastname: Killian
authors.forename: C B
authors.initials: CB
authors.lastname: Salling
authors.forename: Anthony T
authors.initials: AT
authors.lastname: Young
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Marcus
authors.forename: Andreas
authors.initials: A
authors.lastname: Scholl
authors.forename: Andrew
authors.initials: A
authors.lastname: Doran
authors.forename: Catherine
authors.initials: C
authors.lastname: Jenkins
authors.forename: Hans A
authors.initials: HA
authors.lastname: Bechtel
authors.forename: Pupa U P A
authors.initials: PU
authors.lastname: Gilbert
mesh_terms: D002119:Calcium Carbonate / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D008903:Minerals / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D008903:Minerals; D002119:Calcium Carbonate; D010100:Oxygen