--- title: "What Does Science Tell Us About Pearls?" description: "The science of pearls: how mollusks build nacre, why pearls shine, their physical properties, and how chemistry and X-rays reveal a pearl's origin." canonical_url: "https://learnaboutpearls.com/science/" 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 Does Science Tell Us About Pearls? **Short answer:** Science explains pearls as biomineralization: a mollusk's mantle cells lay down calcium carbonate and protein in thin layers, the same way they build the shell's lining. Those layers reflect light, which is why natural and cultured pearls shine. The same structure lets labs read a pearl's history, using chemistry to tell freshwater from saltwater and X-ray imaging to see whether a bead is inside. Pearls sit where biology, chemistry and physics meet. This section explains what science has learned about how pearls are built and how labs read them. ## How mollusks build nacre [Nacre](https://learnaboutpearls.com/glossary/#nacre) is secreted by the [mantle](https://learnaboutpearls.com/glossary/#mantle) of certain [mollusks](https://learnaboutpearls.com/glossary/#mollusk), some [bivalves](https://learnaboutpearls.com/glossary/#bivalve) and some [gastropods](https://learnaboutpearls.com/glossary/#gastropod). It is built from layers of microscopic platelets of [aragonite](https://learnaboutpearls.com/glossary/#aragonite), a form of calcium carbonate, bound together by a fine network of a protein called [conchiolin](https://learnaboutpearls.com/glossary/#conchiolin). The same material lines the inside of the shell. [1] The pages [nacre](https://learnaboutpearls.com/basics/nacre/) and [pearl-producing mollusks](https://learnaboutpearls.com/science/pearl-producing-mollusks/) go further. Inside a pearl, the cells that make nacre form a closed pocket, the [pearl sac](https://learnaboutpearls.com/glossary/#pearl-sac). In the black-lipped [pearl oyster](https://learnaboutpearls.com/glossary/#pearl-oyster), the sac grows around a [cultured pearl](https://learnaboutpearls.com/glossary/#cultured-pearl)’s bead within 14 days, and the first nacre appears about 32 days after [grafting](https://learnaboutpearls.com/glossary/#grafting). [2] The page [how pearls form](https://learnaboutpearls.com/basics/how-pearls-form/) follows the whole process. ## Why pearls shine A pearl’s [luster](https://learnaboutpearls.com/glossary/#luster) comes from light reflected off its surface and off the concentric layers of nacre inside it, which GIA compares to light bouncing off a convex mirror. [3] The layered structure also produces two optical effects: [overtone](https://learnaboutpearls.com/glossary/#overtone), translucent color lying over the pearl’s main [bodycolor](https://learnaboutpearls.com/glossary/#body-color), and [orient](https://learnaboutpearls.com/glossary/#orient), a shimmer of iridescent rainbow colors on or just below the surface. [1, 4] Thin nacre shines less. GIA notes that a bead visible under the nacre, or a dull, chalky look, means the nacre is thin, which affects both luster and durability. [4] ## A pearl’s physical properties GIA’s gem encyclopedia records these properties for pearl. | Property | Value | | ---------------- | ------------------------------ | | Chemistry | Calcium carbonate (CaCO₃) [3] | | Refractive index | 1.52 to 1.69 [3] | | Specific gravity | 2.60 to 2.85 [3] | | Mohs hardness | 2.5 to 3.0 [3] | ## What chemistry reveals The water a pearl grew in leaves a trace in its chemistry. [Freshwater pearls](https://learnaboutpearls.com/glossary/#freshwater-cultured-pearl) contain more manganese and barium, and less sodium, magnesium and strontium, than [saltwater pearls](https://learnaboutpearls.com/glossary/#saltwater-pearl). Labs measure these elements directly, and also through [X-ray luminescence](https://learnaboutpearls.com/glossary/#x-ray-luminescence), which brightens with manganese. [5] Color has a chemistry too. A reflectance feature at 700 nm is a key identifying sign of pearls from the black-lipped pearl oyster, the mollusk of [Tahitian cultured pearls](https://learnaboutpearls.com/glossary/#tahitian-cultured-pearl). [6] Spectroscopy also helps separate natural golden color from color produced by heat or dye. [7, 8] ## What X-rays reveal [X-ray radiography](https://learnaboutpearls.com/glossary/#x-radiography) and [X-ray computed microtomography](https://learnaboutpearls.com/glossary/#computed-microtomography) are central to identifying pearls. [9] A [natural pearl](https://learnaboutpearls.com/glossary/#natural-pearl) shows no bead or curved cavity in its center, and a uniform, onion-like structure. [2] GIA also uses real-time microradiography to measure the [nacre thickness](https://learnaboutpearls.com/glossary/#nacre-thickness) of [bead-cultured pearls](https://learnaboutpearls.com/glossary/#beaded-cultured-pearl) when the nacre looks thin or a client asks. [10] ## Start here 1. [Pearl-producing mollusks](https://learnaboutpearls.com/science/pearl-producing-mollusks/) ## Every page in this section - [Pearl-producing mollusks](https://learnaboutpearls.com/science/pearl-producing-mollusks/) The pearl oysters, mussels, clams, conchs and other mollusks that produce pearls. ## References 1. 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) 2. 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) 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. Gemological Institute of America (GIA), Gem Encyclopedia. Pearl Quality Factors. [Source](https://www.gia.edu/pearl-quality-factor) · [Archived copy](https://web.archive.org/web/20261016075647/https://www.gia.edu/pearl-quality-factor) 5. Stefanos Karampelas and others (2019). Chemical Characteristics of Freshwater and Saltwater Natural and Cultured Pearls from Different Bivalves. [Source](https://www.mdpi.com/2075-163X/9/6/357) · DOI [10.3390/min9060357](https://doi.org/10.3390/min9060357) · [Archived copy](https://web.archive.org/web/20261012102331/https://www.mdpi.com/2075-163X/9/6/357) 6. Artitaya Homkrajae (2016). Spectral Characteristics of Pinctada mazatlanica and Pinctada margaritifera Pearl Oyster Species. [Source](https://www.gia.edu/gems-gemology/summer-2016-gemnews-spectral-characteristics-pinctada-mazatlanica-margaritifera-pearl-oyster-species) · [Archived copy](https://web.archive.org/web/20260317034153/https://www.gia.edu/gems-gemology/summer-2016-gemnews-spectral-characteristics-pinctada-mazatlanica-margaritifera-pearl-oyster-species) 7. Shane Elen (2001). Spectral Reflectance and Fluorescence Characteristics of Natural-Color and Heat-Treated "Golden" South Sea Cultured Pearls. [Source](https://www.gia.edu/gems-gemology/summer-2001-heat-treated-golden-south-sea-cultured-pearls-elen) · DOI [10.5741/GEMS.37.2.114](https://doi.org/10.5741/GEMS.37.2.114) · [Archived copy](https://web.archive.org/web/20260308065638/https://www.gia.edu/gems-gemology/summer-2001-heat-treated-golden-south-sea-cultured-pearls-elen) 8. Chunhui Zhou, Artitaya Homkrajae, Joyce Wing Yan Ho, Akira Hyatt and Nicholas Sturman (2012). Update on the Identification of Dye Treatment in Yellow or "Golden" Cultured Pearls. [Source](https://www.gia.edu/gems-gemology/winter-2012-cultured-pearls-zhou) · DOI [10.5741/GEMS.48.4.284](https://doi.org/10.5741/GEMS.48.4.284) · [Archived copy](https://web.archive.org/web/20260309094817/https://www.gia.edu/gems-gemology/winter-2012-cultured-pearls-zhou) 9. Chunhui Zhou and W. Henry Towbin (2024). Applications of X-Ray Radiography and X-Ray Computed Microtomography in Gemology. [Source](https://www.gia.edu/gems-gemology/winter-2024-x-ray-imaging) · DOI [10.5741/GEMS.60.4.582](https://doi.org/10.5741/GEMS.60.4.582) · [Archived copy](https://web.archive.org/web/20260313113455/https://www.gia.edu/gems-gemology/winter-2024-x-ray-imaging) 10. 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) **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 Does Science Tell Us About Pearls?_ Learn About Pearls. https://learnaboutpearls.com/science/ **MLA:** “What Does Science Tell Us About Pearls?” _Learn About Pearls_, Unique Pearl, November 4, 2026, learnaboutpearls.com/science/. **Chicago:** Learn About Pearls editors. “What Does Science Tell Us About Pearls?” Learn About Pearls. Unique Pearl. Last modified November 4, 2026. https://learnaboutpearls.com/science/. **BibTeX:** `@misc{lap-science, title = {What Does Science Tell Us About Pearls?}, author = {{Learn About Pearls editors}}, year = {2026}, howpublished = {\url{https://learnaboutpearls.com/science/}}, 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. - [Nacre](https://learnaboutpearls.com/basics/nacre/): The layered material pearls and shell linings are made of, and how it differs from mother-of-pearl. - [Identification](https://learnaboutpearls.com/identification/): Telling real from imitation and natural from cultured, spotting treatments, and when to ask a lab.