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.

Solid‐State Transformation of Amorphous Calcium Carbonate to Aragonite Captured by CryoTEM

“…While our reaction conditions are significantly different from those used by organisms during biomineralization, our results demonstrate that this non‐classical pathway is a possible route for the precipitation of aragonite. The similarity of the particle attachment mechanisms observed in forming biominerals4d, 9e, 15 and in vitro suggests that a similar mechanism is indeed possible in biogenic systems. Further work is required to confirm this hypothesis.…”

In-situ liquid phase TEM observations of nucleation and growth processes

“…However, a number of investigations have concluded that the non-classical growth mechanism of aggregation and coalescence of nanoparticles is a common phenomenon in biomineral [90][91][92], biomimetic [93][94][95], environmental [95][96][97], and synthetic systems [8,60,[98][99][100][101][102][103][104][105][106]. The resulting crystals can exhibit complex morphologies such as quasi-one dimensional chains, highly branched nanowires, and 3D hierarchical and self-similar superstructures [107].…”

Anisotropic Lattice Distortions in Biogenic Minerals Originated from Strong Atomic Interactions at Organic/Inorganic Interfaces

“…[66] In sea urchin spines, ACC is transformed into calcite; however, systematic investigations of sea urchin spines resulted in the discovery of different kinds of ACC and uncovering their stabilization mechanisms. [75] Furthermore, there are indications that the amorphous calcium phosphate phase, which is the major mineral phase in the newly formed parts of the zebrafish fin bone, is a precursor of crystalline carbonated hydroxyapatite. [72,73] Later on, an amorphous layer, covering nacre lamellae, was observed in Haliotis laevigata abalone shells.…”