perlmutt

Perlmutt, known in English as nacre, is the iridescent inner layer of shells of many mollusks, especially pearl oysters (family Pteriidae) and some freshwater mussels. It is formed by microscopic platelets of calcium carbonate (primarily aragonite) held together by an organic matrix of proteins and polysaccharides. The nacreous layer is characterized by a brick-and-mortar microstructure: aragonite platelets stacked in layers, interleaved with organic macromolecules, which gives both toughness and the characteristic pearly luster.

The optical effect, often described as iridescence or opalescence, arises from light interference at nanoscale thickness and the regular spacing of platelets. The nacre is secreted by the mollusk’s mantle as a protective lining for the shell, helping to seal irritants. Pearls form when an irritant or seed becomes embedded in the mantle tissue, and successive nacre layers gradually enclose it.

Perlmutt is harvested commercially from pearl oysters (including Pinctada margaritifera, Pinctada maxima) and some freshwater mussels; it is used in jewelry, decorative inlays, buttons, and musical instrument veneers, and occasionally in cosmetic products. Cultured pearl production relies on controlled introduction of a nucleus, followed by layering of nacre.

Sustainability concerns exist due to habitat loss and overharvesting in some regions, though pearl farming has established industry standards and breeding programs. In addition to its natural occurrence, nacre is studied for biomimetic materials because of its combination of strength and toughness.