English: Formation of non–bead-cultured Akoya “keshi” pearls produced in a P. i. fucata mollusk. (A) Optical overview of a nonbeaded keshi–cultured pearl showing iridescence. (B) Cross-section showing CaCO3 growth begins onto an organic center. (C) Mature nacre (purple box in B) showing the ordered state in their thickness and interface curvature. (D and E) Atomic-resolution image of atoms in nacre and its corresponding Fourier transform indicating highly crystalline nacre. (F) Transition from spherulitic aragonite structures to nacre. (G and H) Aggregated nanoparticles form massive aragonite. (I) Formation of nacre begins directly on massive aragonite. Published under CC-license in PNAS 2021 118 (42) e2107477118; https://doi.org/10.1073/pnas.2107477118