Crystal nucleation and near-epitaxial growth in nacre

Nacre is the iridescent inner lining of many mollusk shells, with a unique lamellar structure at the sub-micron scale, and remarkable resistance to fracture. Despite extensive studies, nacre formation mechanisms remain incompletely understood. Here we present 20-nm, 2°-resolution polarization-depend...

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Bibliographic Details
Published in:Journal of structural biology 2013-12, Vol.184 (3), p.454-463
Main Authors: Olson, Ian C., Blonsky, Adam Z., Tamura, Nobumichi, Kunz, Martin, Pokroy, Boaz, Romao, Carl P., White, Mary Anne, Gilbert, Pupa U.P.A.
Format: Article
Language:English
Subjects:
Animal Shells - chemistry
Animal Shells - ultrastructure
Animals
Aragonite
Biomineral
Bridge tilting
Diffraction
Epitaxial
Epitaxy
Finite Element Analysis
Image Processing, Computer-Assisted
Low-angle grain boundary
Mesocrystal
Micro-X-ray
Mollusca
Nacre - analysis
Nacre - chemistry
PEEM
Photoelectron Spectroscopy - methods
PIC-mapping
Tablet
XANES
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Summary:Nacre is the iridescent inner lining of many mollusk shells, with a unique lamellar structure at the sub-micron scale, and remarkable resistance to fracture. Despite extensive studies, nacre formation mechanisms remain incompletely understood. Here we present 20-nm, 2°-resolution polarization-dependent imaging contrast (PIC) images of shells from 15 mollusk species, mapping nacre tablets and their orientation patterns. These data show where new crystal orientations appear and how similar orientations propagate as nacre grows. In all shells we found stacks of co-oriented aragonite (CaCO3) tablets arranged into vertical columns or staggered diagonally. Near the nacre-prismatic (NP) boundary highly disordered spherulitic aragonite is nucleated. Overgrowing nacre tablet crystals are most frequently co-oriented with the underlying aragonite spherulites, or with another tablet. Away from the NP-boundary all tablets are nearly co-oriented in all species, with crystal lattice tilting, abrupt or gradual, always observed and always small (plus or minus 10°). Therefore aragonite crystal growth in nacre is near-epitaxial. Based on these data, we propose that there is one mineral bridge per tablet, and that “bridge tilting” may occur without fracturing the bridge, hence providing the seed from which the next tablet grows near-epitaxially.
ISSN:1047-8477
1095-8657
DOI:10.1016/j.jsb.2013.10.002