The Mesoscale Crystallinity of Nacreous Pearls

TL;DR

This study reveals that nacre in pearls exhibits medium-range mesoscale periodicity with a correlation length of about 16 tablets, and its growth process is influenced by stochastic external factors, contributing to its structural resilience.

Contribution

It provides the first high-resolution characterization of nacre's mesoscale structure and uncovers the stochastic processes influencing its formation, highlighting a universal growth behavior.

Findings

Nacre shows medium-range mesoscale periodicity (~16 tablets).

Growth mechanisms actively correct disorder and defects.

Nacre's growth spectrum follows a universal f^(-1.5) behavior.

Abstract

A pearl's distinguished beauty and toughness are attributable to the periodic stacking of aragonite tablets known as nacre. Nacre has naturally occurring mesoscale periodicity that remarkably arises in the absence of discrete translational symmetry. Gleaning the inspiring biomineral design of a pearl requires quantifying its structural coherence and understanding the stochastic processes that influence formation. By characterizing the entire structure of pearls (~3 mm) in cross-section at high resolution, we show nacre has medium-range mesoscale periodicity. Self-correcting growth mechanisms actively remedy disorder and topological defects of the tablets and act as a countervailing process to long-range disorder. Nacre has a correlation length of roughly 16 tablets (~5.5 um) despite persistent fluctuations and topological defects. For longer distances (> 25 tablets, ~8.5 um), the frequency spectrum of nacre tablets follows f^(-1.5) behavior suggesting growth is coupled to external stochastic processes-a universality found across disparate natural phenomena which now includes pearls.