What is nacre in pearls?
Last updated 17 October 2026
Nacre is a layered material produced by some molluscs, made mainly of microscopic aragonite tablets with thin organic layers between them. It forms the mother-of-pearl lining of many shells and the nacreous material of many natural and cultured pearls. Light interacting with those layers contributes to its shimmering appearance. Not every pearl is nacreous: conch and melo pearls, for example, have different structures.
What the layers do
Aragonite is a crystalline form of calcium carbonate. Light reflected from different layers can interfere, contributing to nacre’s changing colours. The thickness of each microscopic tablet is different from the total nacre coating around a bead. An enlarged schematic shows the arrangement, not stripes visible on an ordinary pearl.
Pearls do not all have the same centre
Some cultured pearls grow nacre around an inserted bead; others are cultured without one. Natural pearls form without human intervention. These origins and internal structures cannot be read from a pearl-like sheen alone. A laboratory may use radiography and other tests to investigate them.
Quality is more than thickness
GIA expanded its nacre classification in May 2025 to five ranges, from Excellent to Poor. It considers layering continuity, condition and relevant thickness standards. This quality description is separate from a millimetre measurement. For bead-cultured pearls, average nacre thickness can be requested on GIA Pearl Identification or Pearl Identification and Classification reports. GIA states that nacre too thin to sustain normal wear is disclosed in report comments.
Frequently asked questions
- Why does nacre thickness matter in pearls?
- In a nacreous bead-cultured pearl, nacre is deposited around the inserted nucleus. A coating that is too thin can affect appearance and durability. Thickness is only one part of nacre quality: layering, continuity, condition and treatments also matter. A thicker coating does not by itself establish a higher lustre grade or a better pearl overall.
- Is nacre the same as mother of pearl?
- Mother of pearl is nacre from the inner shell lining. The same type of material occurs in nacreous pearls, but a piece cut from a shell is not a natural or cultured pearl. Nacre names the material; mother of pearl usually describes it in its shell form.
- Can nacre be damaged by water or chemicals?
- Pearls can be scratched and damaged by acids, perfume, hairspray and other chemicals. Water is not automatically harmful: GIA allows occasional cleaning in warm, soapy water, but advises against ultrasonic and steam cleaners. Let a strung piece dry completely before wearing it, and follow care advice for any adhesive, coating or other material in the jewellery.
Sources and further reading
- Salman and colleagues: nacre layers and optical interference
- GIA: nacreous and non-nacreous pearl structures
- GIA: natural, bead-cultured and non-bead-cultured pearls
- GIA: expanded nacre quality scale, May 2025
- GIA: nacre quality versus an optional thickness measurement
- GIA: pearl care and cleaning
- GIA: how laboratories examine pearl identity and structure
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