--- title: "What Is a Pearl?" description: "What a pearl is, what it is made of, and how natural, cultured and imitation pearls differ, with the definitions used by the FTC and CIBJO." canonical_url: "https://learnaboutpearls.com/basics/" last_updated: "2026-11-04" last_reviewed: "2026-10-26" reviewed_by: "Simon" publisher: "Unique Pearl" publisher_disclosure: "Learn About Pearls is published by Unique Pearl, a pearl jeweler." --- # What Is a Pearl? **Short answer:** A pearl is a hard, usually rounded gem that grows inside a living mollusk, such as an oyster or a mussel. It is made mostly of calcium carbonate, laid down in thin layers held together by organic material. A natural pearl forms with no human help. A cultured pearl forms after a person places a bead or a piece of tissue inside the mollusk. An imitation pearl is manufactured and only looks like a pearl. Every pearl, whether a [natural pearl](https://learnaboutpearls.com/glossary/#natural-pearl) or a [cultured pearl](https://learnaboutpearls.com/glossary/#cultured-pearl), is grown by a living [mollusk](https://learnaboutpearls.com/glossary/#mollusk). This section covers what pearls are made of, how they form, and the words used for the different kinds. ## What a pearl is made of A pearl is made of calcium carbonate and organic material, laid down in concentric layers inside a mollusk. [1] In most pearls used in jewelry, those layers are [nacre](https://learnaboutpearls.com/glossary/#nacre): microscopic platelets of [aragonite](https://learnaboutpearls.com/glossary/#aragonite) bound together by a protein called [conchiolin](https://learnaboutpearls.com/glossary/#conchiolin). That layered structure produces the optical effects called [orient](https://learnaboutpearls.com/glossary/#orient) and [overtone](https://learnaboutpearls.com/glossary/#overtone). [2] GIA records pearl’s chemistry as calcium carbonate and its hardness as 2.5 to 3.0 on the Mohs scale. [3] French Polynesia’s pearl law puts the nacre of [Tahitian cultured pearls](https://learnaboutpearls.com/glossary/#tahitian-cultured-pearl) at about 92% aragonite and 6% conchiolin, with the rest mineral salts and water. [4] ## Natural, cultured and imitation pearls Three words cover almost every pearl you will see for sale: - **Natural pearls** form inside a mollusk with no human help of any kind, usually around a microscopic irritant. [5] They can be nacreous or non-nacreous. [2] The [natural pearls](https://learnaboutpearls.com/natural-pearls/) section covers them. - **Cultured pearls** form after a person starts the process. A technician places a [shell bead](https://learnaboutpearls.com/glossary/#bead) with a piece of [mantle](https://learnaboutpearls.com/glossary/#mantle) tissue in the mollusk, or tissue alone, and the mollusk coats it with nacre. [5] Cultured pearl farming now supports industries in more than 30 countries. [6] - **[Imitation pearls](https://learnaboutpearls.com/glossary/#imitation-pearl)** are manufactured products, made of any material, that only look like a pearl or cultured pearl. [1] In the United States, the unqualified word “pearl” means a natural pearl. A cultured pearl has to be called “cultured” or “cultivated”, and an imitation “imitation”, “artificial” or “simulated”, in letters as clear as the word “pearl”. [1] CIBJO, the international jewelry confederation, requires the same words, “cultured” for cultured pearls and “imitation” for imitations, and recommends labeling natural pearls as “natural pearls”. [2] The page [natural, cultured and imitation pearls](https://learnaboutpearls.com/basics/natural-cultured-and-imitation-pearls/) explains the terms and the rules for using them, and [natural vs cultured pearls](https://learnaboutpearls.com/compare/natural-vs-cultured-pearls/) compares the first two side by side. The page [pearl myths](https://learnaboutpearls.com/basics/pearl-myths/) checks popular beliefs against the evidence. ## Is a pearl a gemstone? Yes, although it is an organic gem grown by an animal rather than a mineral. GIA lists pearl in its gem encyclopedia, [3] and its laboratory has identified and classified natural and cultured pearls since 1949. [7] Pearl is also a birthstone for June, together with alexandrite and moonstone. [8] The page [June birthstone](https://learnaboutpearls.com/wearing/june-birthstone/) tells that story. ## Which animals make pearls Pearls valued as gems come mainly from marine [pearl oysters](https://learnaboutpearls.com/glossary/#pearl-oyster) and freshwater mussels. [Akoya](https://learnaboutpearls.com/glossary/#akoya) cultured pearls grow in the Akoya pearl oyster, [South Sea cultured pearls](https://learnaboutpearls.com/glossary/#south-sea-cultured-pearl) in _[Pinctada maxima](https://learnaboutpearls.com/glossary/#pinctada-maxima)_ and Tahitian cultured pearls in _[Pinctada margaritifera](https://learnaboutpearls.com/glossary/#pinctada-margaritifera)_. [5] Most [freshwater cultured pearls](https://learnaboutpearls.com/glossary/#freshwater-cultured-pearl) come from China, from mussels such as _[Hyriopsis cumingii](https://learnaboutpearls.com/glossary/#hyriopsis-cumingii)_ and its hybrids. [5, 9] The [pearl types](https://learnaboutpearls.com/types/) section covers each one. ## Start here 1. [How pearls form](https://learnaboutpearls.com/basics/how-pearls-form/) 2. [Natural, cultured and imitation](https://learnaboutpearls.com/basics/natural-cultured-and-imitation-pearls/) 3. [Nacre](https://learnaboutpearls.com/basics/nacre/) 4. [Pearl myths](https://learnaboutpearls.com/basics/pearl-myths/) ## Every page in this section - [How pearls form](https://learnaboutpearls.com/basics/how-pearls-form/) How natural and cultured pearls grow inside a mollusk, layer by layer. - [Natural, cultured and imitation](https://learnaboutpearls.com/basics/natural-cultured-and-imitation-pearls/) What the words natural, cultured and imitation mean on a pearl, and the rules for using them. - [Nacre](https://learnaboutpearls.com/basics/nacre/) The layered material pearls and shell linings are made of, and how it differs from mother-of-pearl. - [Pearl myths](https://learnaboutpearls.com/basics/pearl-myths/) Old and new beliefs about pearls, and what the facts say. ## References 1. U.S. Federal Trade Commission (Electronic Code of Federal Regulations). 16 CFR Part 23, Guides for the Jewelry, Precious Metals, and Pewter Industries. [Source](https://www.ecfr.gov/current/title-16/chapter-I/subchapter-B/part-23) · [Archived copy](https://web.archive.org/web/20260907072405/https://www.ecfr.gov/current/title-16/chapter-I/subchapter-B/part-23) 2. CIBJO, The World Jewellery Confederation, Pearl Commission (2026). The CIBJO Pearl Book (Pearl Blue Book) 2026. [Source](https://cibjo.org/wp-content/uploads/2026/10/Pearl-Blue-Book-2026-.pdf) · [Archived copy](https://web.archive.org/web/20261025235254/https://cibjo.org/wp-content/uploads/2026/10/Pearl-Blue-Book-2026-.pdf) 3. Gemological Institute of America (GIA), Gem Encyclopedia. Pearl. [Source](https://www.gia.edu/pearl) · [Archived copy](https://web.archive.org/web/20260909031512/https://www.gia.edu/pearl) 4. Assemblée de la Polynésie française (Journal officiel de la Polynésie française) (2017). Loi du pays n° 2017-16 du 18 juillet 2017 réglementant les activités professionnelles liées à la production et la commercialisation des produits perliers et nacriers en Polynésie française. [Source](https://www.ressources-marines.gov.pf/wp-content/uploads/sites/24/2017/10/Loi-du-Pays-n%C2%B0-2017-16-du-18_07_2017-Activit%C3%A9s-professionnelles-perli.pdf) · [Archived copy](https://web.archive.org/web/20261026000126/https://www.ressources-marines.gov.pf/wp-content/uploads/sites/24/2017/10/Loi-du-Pays-n%C2%B0-2017-16-du-18_07_2017-Activit%C3%A9s-professionnelles-perli.pdf) 5. Gemological Institute of America (GIA), Gem Encyclopedia. Pearl Description. [Source](https://www.gia.edu/pearl-description) · [Archived copy](https://web.archive.org/web/20261017085317/https://www.gia.edu/pearl-description) 6. Changbo Zhu, Paul C. Southgate and Ting Li (2019). Production of Pearls. [Source](https://link.springer.com/chapter/10.1007/978-3-319-96776-9_5) · DOI [10.1007/978-3-319-96776-9_5](https://doi.org/10.1007/978-3-319-96776-9_5) · [Archived copy](https://web.archive.org/web/20240129152149/https://link.springer.com/chapter/10.1007/978-3-319-96776-9_5) 7. Gemological Institute of America (GIA), Analysis & Grading. How GIA Identifies and Classifies Pearls. [Source](https://www.gia.edu/gem-lab-how-gia-identifies-classifies-pearls) · [Archived copy](https://web.archive.org/web/20260606232640/https://www.gia.edu/gem-lab-how-gia-identifies-classifies-pearls) 8. Gemological Institute of America (GIA), Birthstones. June Birthstones. [Source](https://www.gia.edu/birthstones/june-birthstones) · [Archived copy](https://web.archive.org/web/20260614074112/https://www.gia.edu/birthstones/june-birthstones) 9. Phoebe Shang (2026). Freshwater Akoyas – A Trending Misnomer for Certain Freshwater Pearls. [Source](https://www.gia.edu/freshwater-akoyas-a-trending-misnomer-for-certain-pearls) · [Archived copy](https://web.archive.org/web/20260617073835/https://www.gia.edu/freshwater-akoyas-a-trending-misnomer-for-certain-pearls) **Written by:** Learn About Pearls editors **Fact-checked:** Learn About Pearls editors, October 26, 2026 **Reviewed by:** Simon, October 26, 2026 **First published:** November 4, 2026 **Publisher:** [Unique Pearl](https://learnaboutpearls.com/about/), a pearl jeweler **Revision history** 1. November 4, 2026: First published. First published **How to cite this page** **APA:** Learn About Pearls editors. (2026). _What Is a Pearl?_ Learn About Pearls. https://learnaboutpearls.com/basics/ **MLA:** “What Is a Pearl?” _Learn About Pearls_, Unique Pearl, November 4, 2026, learnaboutpearls.com/basics/. **Chicago:** Learn About Pearls editors. “What Is a Pearl?” Learn About Pearls. Unique Pearl. Last modified November 4, 2026. https://learnaboutpearls.com/basics/. **BibTeX:** `@misc{lap-basics, title = {What Is a Pearl?}, author = {{Learn About Pearls editors}}, year = {2026}, howpublished = {\url{https://learnaboutpearls.com/basics/}}, note = {Learn About Pearls, published by Unique Pearl}}` Quoting with attribution and a link is welcome. See [how to cite and reuse](https://learnaboutpearls.com/cite/). **Suggest a correction** ## Related pages - [How pearls form](https://learnaboutpearls.com/basics/how-pearls-form/): How natural and cultured pearls grow inside a mollusk, layer by layer. - [Natural vs cultured](https://learnaboutpearls.com/compare/natural-vs-cultured-pearls/): How pearls that formed on their own differ from pearls that people started. - [Pearl-producing mollusks](https://learnaboutpearls.com/science/pearl-producing-mollusks/): The pearl oysters, mussels, clams, conchs and other mollusks that produce pearls. - [Pearl types](https://learnaboutpearls.com/types/): Akoya, freshwater, South Sea, Tahitian and keshi pearls, and where each one comes from.