Atomic force microscopy of the nacreous layer in mollusc shells

Abstract

We present atomic force microscopy (afm) observations of the aragonite tablets of mature nacre in two types of mollusc, a bivalve ( A t r i n as p.) and a gastropod ( rufescens). By imaging in liquids it was possible to dissolve away the nacre layer by layer to reveal both the structure of a single tablet and its relation to vertically adjacent tablets. Atrina tablets (inner face) had a concave appearance; the central depression was surrounded by elongate rings that mimicked the orientation and aspect ratio of the unit cell viewed along the c axis. The tablet surfaces had a rough texture, and flat (001) planes of aragonite were rarely observed. Unit cell orientations were generally aligned both vertically and laterally between tablets of Atrina. Etching tablets with HC1 initially removed the elongate rings and produced etch rows parallel to the a axis. Further etching of bleached Atrina nacre lifted off individual tablets to reveal underlying nacreous layers, showing no morphological registry between vertically adjacent tablets. The nacreous structure of Haliotis differed from Atrina in three ways: (i) the tablets were flatter and showed no elongate rings; (ii) the positions of the central depressions approximately repeated between nacreous layers, showing that the (presumed) nucleation sites line up along a given stack; and (iii) the unit cell orientations were not preserved between laterally adjacent tablets but were approximately aligned between vertically adjacent tablets.

Study on the Microstructure of the Pinctada martensii Pearls and Its Significance

“…Aragonites can be aggregated to form aragonite tablets (the size is about 0.4 ∼ 2 μm, the diameter is about 3 ∼ 10 μm), and aragonite microlayers in the next. During a long period of time, the aragonite tablets had been believed to be directional arrangement and their C-crystal axis was only vertical to the stratification plane of the nacres [10]. Namely, the crystalline orientation of aragonite tablets is unique because they were crystallized along with the crystalline plane nets which were matching with the formation periods of the organic matters.…”

Organization pattern of nacre in Pteriidae (Bivalvia: Mollusca) explained by crystal competition

“…The direction of a crystal on a new layer is determined by that of the crystal of the previous layer onto which it begins to grow. In this way, we reproduce the effect of epitaxial growth, which is well established in bivalve and gastropod nacre (Manne et al 1994;Schäffer et al 1997). Finally, the program also provides the histogram of angle frequency at intervals of 108 and the mean angle between the b-axis and the growth direction (alignment of b-axis).…”

“…In Gastropoda, nacre crystals stack in towers that finally coalesce by lateral growth (Wise 1970;Nakahara 1983Nakahara , 1991. Crystals of a same tower have their crystallographic axes co-oriented, with the c-axis along the stacking axis (Manne et al 1994). Crystals in different towers have their c-axes aligned but the a-and b-axes have an azimuthal disorder (turbostratic disposition ;Schmidt 1923;Wada 1961;Wise 1970).…”

Molecular Cloning and Characterization of Lustrin A, a Matrix Protein from Shell and Pearl Nacre of Haliotis rufescens

“…The thickness of the mineral tablets apparently is determined by the matrix sheets (22), while their interdigitation is controlled, in part, by the stochastic location of nanopores in the stencillike sheets through which the crystals grow from one layer to the next (32,(35)(36)(37)(38). Electron microscopy, x-ray, and electron diffraction have shown that each sheet consists of a chitin-like core sandwiched between two layers of protein (12, 28 -30).…”