Crystallographic control on the substructure of nacre tablets.
Nacre tablets of mollusks develop two kinds of features when either the calcium carbonate or the organic portions are removed: (1) parallel lineations (vermiculations) formed by elongated carbonate rods, and (2) hourglass patterns, which appear in high relief when etched or in low relief if bleached. In untreated tablets, SEM and AFM data show that vermiculations correspond to aligned and fused aragonite nanogloblules, which are partly surrounded by thin organic pellicles. EBSD mapping of the surfaces of tablets indicates that the vermiculations are invariably parallel to the crystallographic a-axis of aragonite and that the triangles are aligned with the b-axis and correspond to the advance of the {010} faces during the growth of the tablet. According to our interpretation, the vermiculations appear because organic molecules during growth are expelled from the a-axis, where the Ca-CO3 bonds are the shortest. In this way, the subunits forming nacre merge uninterruptedly, forming chains parallel to the a-axis, whereas the organic molecules are expelled to the sides of these chains. Hourglass patterns would be produced by preferential adsorption of organic molecules along the {010}, as compared to the {100} faces. A model is presented for the nanostructure of nacre tablets. SEM and EBSD data also show the existence within the tablets of nanocrystalline units, which are twinned on {110} with the rest of the tablet. Our study shows that the growth dynamics of nacre tablets (and bioaragonite in general) results from the interaction at two different and mutually related levels: tablets and nanogranules.
Departamento de Estratigrafía y Paleontología, Facultad de Ciencias, Universidad de Granada, Avenida Fuentenueva s/n, 18071 Granada, Spain. Electronic address: acheca@ugr.es.
Antonio G
AG
Checa
Department of Paleozoology, Swedish Museum of Natural History, Frescativägen 40, 11-418 Stockholm, Sweden. Electronic address: Harry.Mutvei@nrm.se.
Harry
H
Mutvei
Departamento de Estratigrafía y Paleontología, Facultad de Ciencias, Universidad de Granada, Avenida Fuentenueva s/n, 18071 Granada, Spain. Electronic address: tay@ugr.es.
Antonio J
AJ
Osuna-Mascaró
Institute of Metallurgy and Materials Science of the Polish Academy of Sciences, Reymonta. 25, 30-059 Kraków, Poland. Electronic address: j.bonarski@imim.pl.
Jan T
JT
Bonarski
Institute of Metallurgy and Materials Science of the Polish Academy of Sciences, Reymonta. 25, 30-059 Kraków, Poland. Electronic address: marekfaryna@gmail.com.
Marek
M
Faryna
Institute of Metallurgy and Materials Science of the Polish Academy of Sciences, Reymonta. 25, 30-059 Kraków, Poland. Electronic address: marekfaryna@gmail.com.
Katarzyna
K
Berent
Departamento de Cristalografía y Mineralogía, Facultad de Ciencias Geológicas, Universidad Complutense de Madrid, José Antonio Novais s/n, 28040 Madrid, Spain. Electronic address: marekfaryna@gmail.com.
Carlos M
CM
Pina
CNRS, UMR7365, Ingénierie Moléculaire et Physiopathologie Articulaire (IMoPA), Faculté de Médecine, Université de Lorraine, 9 Avenue de la Forêt de Haye, 54505 Vandoeuvre-lès-Nancy, France. Electronic address: rousseam@gmx.net.
Marthe
M
Rousseau
Departamento de Estratigrafía y Paleontología, Facultad de Ciencias, Universidad de Granada, Avenida Fuentenueva s/n, 18071 Granada, Spain. Electronic address: emacias@ugr.es.
Elena
E
Macías-Sánchez
D000818:Animals; D049872:Bivalvia / Q000378:metabolism / Q000648:ultrastructure*; D003460:Crystallization; D018625:Microscopy, Atomic Force; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D060734:Nacre / Q000737:chemistry* / Q000378:metabolism; D013499:Surface Properties
D060734:Nacre
Aragonite; Crystallography; Molluscs; Nacre; Organic molecules