What is nacre in pearls?
By Jared James · Last updated 21 May 2026
Definition
Nacre is the iridescent material that mollusks such as oysters and mussels secrete in thin crystalline layers as a protective coating inside their shells. It is made primarily of aragonite, a form of calcium carbonate, arranged in microscopic layers that diffract light to produce the lustrous shimmer associated with pearls. When an irritant enters a mollusk, it coats it with successive layers of nacre, forming a pearl. Nacre is also what lines the shell itself, which is why it is also called mother of pearl.
Frequently asked questions
- Why does nacre thickness matter in pearls?
- Thicker nacre means a deeper, more complex lustre and a pearl that will wear better over time. Thin nacre can chip or peel, exposing a chalky nucleus underneath. When buying cultured pearls, nacre thickness is an important quality indicator.
- Is nacre the same as mother of pearl?
- Yes, they are the same material. Nacre is the scientific and trade name for the substance, while mother of pearl is the common name for the nacre layer found on the inner surface of the shell. Both terms describe the same iridescent calcium carbonate layers.
- Can nacre be damaged by water or chemicals?
- Nacre is relatively fragile compared with gemstones. Acids, perfume, hairspray and chlorinated water can dull and dissolve the surface over time. Gentle handling and keeping pearls away from chemicals will help maintain the lustre.
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