# Freshwater pearl

- Page: https://taslar.bumba.tr/en/stones/freshwater-pearl/
- Turkish: Tatlı su incisi
- Also known as: Freshwater cultured pearl
- Kind: Variety
- Classification: Organic gems
- Crystal system: Orthorhombic
- Hardness (Mohs): 2.5–3
- Specific gravity: 2.6–2.85 g/cm³
- Refractive index: 1.52–1.69
- Lustre: Pearly
- Transparency: Opaque
- Colours: white, cream, pink, peach, lavender, purple, golden
- Streak: White
- Cleavage: None
- Fracture: Uneven
- Composition: Platelets of calcium carbonate (CaCO₃, mostly aragonite) bound together by an organic substance called conchiolin; this layered material is nacre. Most saltwater cultured pearls have a shell bead nucleus at their centre.
- Texture: Thin layers of nacre stacked concentrically, like the layers of an onion. Under a loupe the surface shows fine, wavy lines, which is why it feels slightly gritty against the teeth.
- Value ladder: 5/9 step, Ornamental stone

A pearl from mussels in lakes and rivers: today mostly grown in China without a bead, nacre all the way through, the most plentiful and varied cultured pearl.

A freshwater pearl forms inside mussels living in lakes, rivers and ponds. For centuries natural freshwater pearls were gathered from the rivers of places such as Scotland and North America, but the mussels that make them are now protected. Almost all freshwater pearls on the market are cultured, and most are grown in China. Most have no shell bead at their centre and are nacre all the way through. With colours from white to pink, peach and lavender and a huge variety of shapes, they are the most plentiful pearls of all.

## How does it form?

A natural freshwater pearl starts when a parasite gets into the mantle tissue between the mussel’s shell and body, or when that tissue is damaged; the mussel then wraps the spot in layers of nacre. Natural pearls are rare, which is why almost all freshwater pearls on the market are cultured.

In a cultured freshwater pearl, people start the process. In China the “triangle sail mussel” (Hyriopsis cumingii) is the most used today. A technician cuts squares of about 3 mm from the mantle of a donor mussel and slips them into small incisions in the mantle of the host mussel. A single mussel can take 25 to 30 pieces, and a pearl grows around each one. The mussels are then kept in lakes and ponds for three to five years. After harvest the pearls are cleaned, sorted by size and shape, pre-treated in chemical solutions and bleached, drilled, and polished with a mixture of cornmeal and wax. In recent years some farms have also used beads to grow larger, rounder pearls.

## What is it used for?

- **Jewellery:** used in necklaces, earrings, bracelets and rings; their wide range of shapes and colours makes them popular in modern designs.
- **Cosmetics and traditional remedies:** pearls are ground into powder for cosmetics and for traditional Chinese medicine.
- **Mother-of-pearl and beads:** freshwater mussel shells were used to make buttons, and the bead nuclei of saltwater cultured pearls are still carved from freshwater mussel shell today.

## Natural freshwater pearls

In Europe the most famous source of natural freshwater pearls was the rivers of Scotland; the River Oykel in the Highlands was noted for the finest rose-pink pearls. The freshwater pearl mussel is now an endangered species, completely protected in all European countries, and pearl fishing has been banned in the United Kingdom since 1998.

## The rise of the cultured pearl

Whole freshwater pearls were first cultured at Lake Biwa in Japan in 1914, but pollution has severely cut that production. In China commercial culture began in Jiangsu and Zhejiang in 1968: output of about 500 kilograms a year in the late 1960s rose to 20 tonnes in 1972 and to more than 2,000 tonnes in 1995 and 1996. In 2006 China’s annual output was around 1,500 tonnes, of which about 800 tonnes were of jewellery quality. In the early 2000s, 95 percent of the freshwater pearls sold in the world came from China.

## In Türkiye

There is no commercial freshwater pearl production in Türkiye. In a study published in 2019, mantle tissue was grafted into four native mussel species (Unio terminalis, Potamida littoralis, Leguminaia wheatleyi and Anodonta pseudodopsis) collected from Lake Gölbaşı in Hatay, and the formation of pearl sacs was examined after three months; Unio terminalis was the most successful species. The study was published as the first research on pearl production in Türkiye.

## How to recognise it

- Most freshwater cultured pearls are grown with a piece of tissue only, so looking into the drill hole shows no boundary of a bead inside; the pearl is nacre throughout.
- Shapes vary widely: ovals, buttons, drops, rice-grain shapes and irregular (baroque) forms are common; perfectly round ones are scarcer.
- Their natural colours are white, cream, pink, peach, lavender and purple. A strand in which every pearl is exactly the same dark or very vivid colour may point to dyeing.
- Telling a freshwater pearl from a saltwater one for certain is a laboratory job, using methods such as X-ray fluorescence.

## Fakes and imitations

- Treated pearls: bleaching is a routine step that freshwater pearls go through after harvest, while irradiation darkens freshwater pearls and shells. Treatments that change the colour should be disclosed by the seller.
- Sold as “natural pearls”: almost all freshwater pearls on the market are cultured; the US Federal Trade Commission requires them to be called “freshwater cultured pearls” in commerce.
- Glass and plastic imitations: they have no nacre and feel smooth when rubbed against the teeth or against each other.

## What determines its value?

Lustre, shape, size, surface quality and colour set the value of a freshwater pearl; perfectly round, large and lustrous ones are the scarcest. Because it is nacre throughout, there is no nacre layer to wear through to a bead, which adds to its durability. With hundreds of tonnes grown in China every year, freshwater cultured pearls are the most affordable pearls. Natural freshwater pearls from the rivers of Scotland or North America, on the other hand, are very rare collector’s pieces. Dyeing and irradiation should be disclosed.

This information is educational, not buying, selling or investment advice. Value varies enormously with quality and treatment.

## Myths and misconceptions

- Myth: A freshwater pearl is not a real pearl but a cheap imitation of a saltwater one. Fact: A freshwater pearl is a real pearl grown from nacre inside a living mussel; most do not even have a bead and are nacre throughout. They are cheap because one mussel yields dozens of pearls and they are produced in vast quantities.
- Myth: Freshwater pearls are always small and misshapen, like grains of rice. Fact: The first Chinese freshwater pearls to reach the world market around 1970 really were small “rice” pearls. Methods have improved since, and round and near-round freshwater pearls of 10–15 mm are grown today.

## What is it believed to be good for?

This section reports beliefs; it is not health information. There is no scientific evidence for these claims and no stone replaces medical treatment.

- In traditional Chinese medicine, ground pearl powder is believed to work as a medicine; according to a study published in Türkiye, the pearls used in the pharmaceutical and cosmetics industries are produced by tissue grafting in freshwater mussels.

What science says: Pearl powder is mostly calcium carbonate, chemically the same substance as chalk and limestone; no medicinal effect beyond that of any ordinary calcium source has been shown scientifically.

## Did you know?

- The Abernethy pearl was found by William Abernethy in Scotland’s River Tay in 1967. Weighing 43.6 grains (2.825 grams), this white pearl with a slightly pink overtone is now on display at the National Museum of Scotland.
- The freshwater pearl mussel (Margaritifera margaritifera) can live for 210–250 years, making it one of the longest-lived animals known.
- The Tennessee River pearl has been Tennessee’s state gem since 1979, and the freshwater pearl Kentucky’s since 1986.
- Lustrous, rosy “Kasumi” pearls, grown over four years in Japan’s Lake Kasumigaura, stopped being produced in 2006 because they could not compete with cheap Chinese pearls.

## Where is it found?

- Zhuji, Zhejiang, China (Major deposit): China’s largest pearl market; Zhejiang is one of the two provinces where freshwater pearl culture began in China in 1968.
- Jiangsu, China (Major deposit): Freshwater pearl culture in China began in Jiangsu and Zhejiang in 1968; today it is also carried out in Anhui, Jiangxi, Fujian, Hunan and Hubei.
- Lake Biwa, Shiga Prefecture, Japan (Historic source): Where whole freshwater pearls were first cultured: M. Fujita began culturing pearls here in the Biwa pearly mussel (Hyriopsis schlegelii) in 1914; pollution has since cut production severely.
- Lake Kasumigaura, Ibaraki Prefecture, Japan (Historic source): Lustrous, rosy “Kasumi” pearls were grown here over four years; unable to compete with cheap Chinese pearls, production stopped in 2006.
- River Tay, Scotland, United Kingdom (Historic source): Natural freshwater pearls: the famous Abernethy pearl was found in this river in 1967 (the point is the city of Perth, on the river). Because the pearl mussel is endangered, pearl fishing has been banned in the UK since 1998.
- Camden area (Kentucky Lake), Tennessee, USA (Known locality): On Kentucky Lake, on the Tennessee River, lies the pearl farm founded by John Latendresse, the only source of freshwater cultured pearls outside Asia; the Tennessee River pearl has been Tennessee’s state gem since 1979.

## Sources

- [Continuity and Change in Chinese Freshwater Pearl Culture (D. Fiske & J. Shepherd), Gems & Gemology 43(2)](https://cms.gia.edu/dam/jcr:d34964af-1ff2-4d67-8b1d-b4c818179151/Continuity-and-Change-in-Chinese-Freshwater-Pearl-Culture.pdf), GIA, 2007
- [Freshwater Pearl Culture in China (Hua Dan, Gu Ruobo & Wen Haibo)](https://www.globalseafood.org/advocate/freshwater-pearl-culture-in-china/), Global Aquaculture Advocate (Global Seafood Alliance), 2003
- [Polynesian Black Pearls (M. Goebel & D. M. Dirlam), Gems & Gemology 25(3)](https://www.gia.edu/dam/migrated-assets/_assets/ba822c74c2bdbdc1-Polynesian-Black-Pearls.pdf), GIA, 1989
- [Pearl Description (Gem Encyclopedia)](https://www.gia.edu/pearl-description), Gemological Institute of America (GIA)
- [Pearl Quality Factors](https://www.gia.edu/pearl-quality-factor), Gemological Institute of America (GIA)
- [Freshwater pearl](https://en.wikipedia.org/wiki/Freshwater_pearl), Wikipedia
- [Pearl](https://en.wikipedia.org/wiki/Pearl), Wikipedia
- [Cultured pearl](https://en.wikipedia.org/wiki/Cultured_pearl), Wikipedia
- [Freshwater pearl mussel](https://en.wikipedia.org/wiki/Freshwater_pearl_mussel), Wikipedia
- [Abernethy Pearl](https://en.wikipedia.org/wiki/Abernethy_Pearl), Wikipedia
- [List of U.S. state minerals, rocks, stones and gemstones](https://en.wikipedia.org/wiki/List_of_U.S._state_minerals,_rocks,_stones_and_gemstones), Wikipedia
- [How Tennessee became home to North America’s only freshwater pearl farm (W. Darnall, WKMS)](https://wpln.org/post/how-tennessee-became-home-to-north-americas-only-freshwater-pearl-farm/), WPLN, 2025
- [Lake Kasumigaura](https://en.wikipedia.org/wiki/Lake_Kasumigaura), Wikipedia
- [Lake Biwa](https://en.wikipedia.org/wiki/Lake_Biwa), Wikipedia
- [Zhuji](https://en.wikipedia.org/wiki/Zhuji), Wikipedia
- [Jiangsu](https://en.wikipedia.org/wiki/Jiangsu), Wikipedia
- [Camden, Tennessee](https://en.wikipedia.org/wiki/Camden,_Tennessee), Wikipedia
- [Perth, Scotland](https://en.wikipedia.org/wiki/Perth,_Scotland), Wikipedia
- [Greft İmplantasyonunda İnci Kesesi Oluşumunun Dört Midye Türünde (Unionidae) Karşılaştırılması (H. Şereflişan), Türk Tarım – Gıda Bilim ve Teknoloji Dergisi 7(10)](https://agrifoodscience.com/index.php/TURJAF/article/download/2820/1297/22435), Turkish Science and Technology Publishing, 2019


Source: https://taslar.bumba.tr/en/stones/freshwater-pearl/ · Licence: CC BY-SA 4.0