Over the past decades, our understanding of nacre's toughening origin has long stayed at the level of crack deflection along the biopolymer interface between aragonite platelets. It has been widely thought that the ceramic aragonite platelets in nacre invariably remain shielded from the propagating crack. Here we report an unexpected experimental observation that the propagating crack, surprisi...

Understanding nacre's bottom-up biomineralization mechanism, particularly, how individual aragonite platelets are formed, has long remained elusive due to its crystallographic peculiarity and structural complexity. Here we report that crystallographic order-disorder transition can be triggered within individual aragonite platelets in pristine nacre by means of heat treatment and/or inelastic de...

Early-stage reaction mechanisms for aragonite-promoting systems are relatively unknown compared to the more thermodynamically stable calcium carbonate polymorph, calcite. Using cryoTEM and SEM, the early reaction stages taking place during aragonite formation were identified in a highly supersaturated solution using an alcohol-water solvent, and an overall particle attachment growth mechanism w...

Needle-like o r b ranch-like a ragonite was prepared from sparingly dissoluble magnesium carbonate and calcium chloride aqueous solution. The morphology, particle size, and aspect ratio of the product were characterized with SEM. The polymorphs and crystal size were characterized with XRD. Comparing with calcium sulfate and sodium carbonate that were used in our previous study, a high reactant ...

We demonstrate direct evidence that a single-crystal-like aragonite platelet is essentially assembled with aragonite nanoparticles. The aragonite nanoparticles are readily oriented and assembled into pseudo-single-crystal aragonite platelets via screw dislocation and amorphous aggregation, which are two dominant mediating mechanisms between nanoparticles during biomineralization. These findings...

Otoliths are calcium carbonate concretions laid down in the inner ear of fish and used in fish age estimation. Otoliths precipitate in the form of aragonite but aberrant precipitation may result in vaterite formation instead of aragonite. Vaterite otoliths are more translucent than aragonite. The quantity of HCl-soluble proteins (SP) was measured in the vaterite otoliths and their aragonite pai...

Calcium carbonate (CaCO3) occurs in two major polymorphs: rhombohedral calcite and orthorhombic aragonite, the latter is thermodynamically metastable. In this study, we first prepared aragonite needle-like particles by introducing CO2-containing gas into Ca(OH)2 aqueous slurry. Then, the resulted aragonite particles were heat treated at 500 ◦C for 1 h, in order to induce the aragonite–calcite p...

Species of Haliotis (abalone) show high variety in structure and mineralogy of the shell. One of the European species (Haliotis tuberculata) in particular has an unusual shell structure in which calcite and aragonite coexist at a microscale with small patches of aragonite embedded in larger calcitic zones. A detailed examination of the boundary between calcite and aragonite using analytical mic...

Vaterite otoliths were sampled from two reared populations (Celtic and Clyde Seas) of juvenile herring Clupea harengus. The crystallography, elemental composition and morphometry were analysed and compared with those of normal aragonite otoliths. The incidence of vaterite otoliths in the juveniles sampled (n1⁄4 601) ranged from 7 8% in the Clyde population to 13 9% in the Celtic Sea population,...

:, ~ varied most significantly with temperature, ranging from limited slip and twinning at 400°C, limited recrystalliza,t ,tion at 500°C, widespread recrystallization at 600 and 7QOoC, to grain growth at 800-900°C. Variations in ! confining pressure from 0.3 to 2.0 GPa have no apparent effect on calcite deformation microstructures. : Aragonite grew in 10-6-10-7 S-l strain rate tests conducted f...