title: Nanoscale Transforming Mineral Phases in Fresh Nacre.
abstract: Nacre, or mother-of-pearl, the iridescent inner layer of many mollusk shells, is a biomineral lamellar composite of aragonite (CaCO3) and organic sheets. Biomineralization frequently occurs via transient amorphous precursor phases, crystallizing into the final stable biomineral. In nacre, despite extensive attempts, amorphous calcium carbonate (ACC) precursors have remained elusive. They were inferred from non-nacre-forming larval shells, or from a residue of amorphous material surrounding mature gastropod nacre tablets, and have only once been observed in bivalve nacre. Here we present the first direct observation of ACC precursors to nacre formation, obtained from the growth front of nacre in gastropod shells from red abalone (Haliotis rufescens), using synchrotron spectromicroscopy. Surprisingly, the abalone nacre data show the same ACC phases that are precursors to calcite (CaCO3) formation in sea urchin spicules, and not proto-aragonite or poorly crystalline aragonite (pAra), as expected for aragonitic nacre. In contrast, we find pAra in coral.
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.affiliation: Department of Physics, University of Wisconsin-Madison , 1150 University Avenue, Madison, Wisconsin 53706, United States.
authors.forename: Chang-Yu
authors.initials: CY
authors.lastname: Sun
authors.affiliation: Advanced Light Source, Lawrence Berkeley National Laboratory , 1 Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Marcus
authors.affiliation: Department of Physics, University of Wisconsin-Madison , 1150 University Avenue, Madison, Wisconsin 53706, United States.
authors.forename: Susan N
authors.initials: SN
authors.lastname: Coppersmith
authors.affiliation: Department of Geosciences, Princeton University , Princeton, New Jersey 08544, United States.
authors.forename: Satish C B
authors.initials: SC
authors.lastname: Myneni
authors.affiliation: Department of Physics, University of Wisconsin-Madison , 1150 University Avenue, Madison, Wisconsin 53706, United States.|Department of Chemistry, University of Wisconsin-Madison , 1101 University Avenue, Madison, Wisconsin 53706, United States.|Radcliffe Institute for Advanced Study, Harvard University , 8 Garden Street, Cambridge, Massachusetts 02138, United States.
authors.forename: Pupa U P A
authors.initials: PU
authors.lastname: Gilbert
mesh_terms: D008855:Microscopy, Electron, Scanning; D008903:Minerals / Q000737:chemistry*; D060734:Nacre / Q000737:chemistry*; D036103:Nanotechnology; D056928:X-Ray Absorption Spectroscopy
chemical_list: D008903:Minerals; D060734:Nacre