Mother of Pearl (Nacre)

Hardness: 2.5-4.5 on Mohs scale; Color: Iridescent white, cream, silver, sometimes with a rainbow sheen; Luster: Pearly, iridescent; Crystal structure: Orthorhombic (aragonite); Cleavage: Indistinct; Specific Gravity: 2.6-2.9

Mother of Pearl is created by certain mollusks (such as oysters and abalones) as an inner shell layer. It is technically a biomineral, not a rock or mineral in the traditional geological sense. It forms as a protective lining inside the shell, continually secreted by the mollusk's mantle tissue. This process involves the deposition of microscopic aragonite crystals in a layered structure, cemented together by an organic protein called conchiolin. It is continuously formed throughout the mollusk's life and has no specific 'geological age' in terms of rock formation, but the shells themselves can be found in sedimentary deposits dating back millions of years.

Extensively used in jewelry (beads, inlays, cabochons), decorative items, buttons, watch faces, musical instrument inlays, and furniture ornamentation. Its iridescent beauty has made it a prized material for centuries.

Nacre is renowned for its resilience and strength, which comes from its hierarchical structure of microscopic aragonite platelets. These layers are stacked and interlocked, providing excellent fracture resistance. This structure also causes the characteristic iridescence, as light interferes with and reflects off the multiple layers. It is the same material that forms pearls.

In the field (or when identifying raw material), look for its characteristic pearly luster and iridescent play of colors, often creamy white to silvery, sometimes with hints of pink, green, or blue. It's relatively soft and can be scratched with a knife. It will react to dilute acids (like vinegar) by effervescing due to its calcium carbonate content. Commonly found in coastal areas and marine environments where large mollusks thrive, collected from oyster shells, abalone shells, and other bivalve and gastropod shells.