Pearls – Formation, Properties and Gemmology
Pearls form through complex biological processes and possess distinctive chemical and physical properties.
This scientifically grounded overview explains the biology of pearl-producing molluscs, the formation and structure of pearls, the history of pearl cultivation and the principles of gemmological assessment. Scientific sources are listed in the relevant chapters.
Biology of Pearl-Producing Molluscs
Pearls are natural formations that develop inside the bodies of certain molluscs (Mollusca). Bivalves (Bivalvia), whose soft bodies are protected by two calcareous shells, are particularly important. Some gastropods (Gastropoda) can also produce pearls.
Not all pearls have the same internal structure. Alongside familiar nacreous pearls, there are pearls whose structure differs considerably from the layered arrangement characteristic of nacre.¹
Two groups of bivalves are of particular importance to traditional nacreous pearl cultivation:
Marine bivalves: the main molluscs used for marine pearl cultivation belong to the genera Pinctada and Pteria. Both are placed within the superfamily Pterioidea, although current zoological classification assigns them to different families: Margaritidae (Pinctada) and Pteriidae (Pteria). Despite the common name “pearl oysters”, these animals are not true oysters of the family Ostreidae.³
Freshwater bivalves: species belonging to the family Unionidae are especially important. Modern freshwater pearl cultivation makes particular use of species of the genus Sinohyriopsis (often assigned to Hyriopsis in older scientific literature). Other pearl-producing families include the Margaritiferidae, to which the European freshwater pearl mussel belongs.² ⁴
Freshwater mussels are often described as river or lake mussels. These terms refer to their habitats rather than separate major zoological groups.
Scientific References
1. Gemological Institute of America (GIA). GIA Pearl Research. Overview of pearl formation and pearl-producing molluscs.
https://www.gia.edu/pearl-research
2. Zhu, C., Southgate, P. C. & Li, T. (2018). Production of Pearls. In: Goods and Services of Marine Bivalves. Springer.
https://doi.org/10.1007/978-3-319-96776-9_5
3. MolluscaBase / World Register of Marine Species (WoRMS). Taxonomic classification of the Ostreidae and the pearl-producing genera Pinctada and Pteria. Continuously updated specialist database.
https://www.marinespecies.org/aphia.php?p=taxlist&tName=Ostreidae
https://www.marinespecies.org/aphia.php?p=taxlist&tName=Pinctada
https://www.marinespecies.org/aphia.php?p=taxlist&tName=Pteria
4. Zhou, Q. et al. (2026). Policy-Driven Sustainability in China’s Freshwater Pearl Culturing Industry. Gems & Gemology, 62(2).
Freshwater Mussels
Freshwater mussels inhabit rivers, streams, lakes and other inland waters. The species most important to pearl formation belong predominantly to the families Margaritiferidae and Unionidae.
They feed mainly by filtering water and extracting microscopic food particles. In doing so, they also contribute to nutrient cycling in aquatic ecosystems.
A notable feature of many freshwater mussels is their reproductive cycle. Their larvae, known as glochidia, require a suitable host fish for part of their development. They attach to its gills or fins, continue developing and subsequently detach as juvenile mussels. They then develop further in the sediment.¹
Only certain species are suitable for commercial pearl cultivation. In addition to the ability to produce nacre, growth rate, resilience, survival and the quality of the nacre produced are decisive factors.
European Freshwater Pearl Mussel – Margaritifera margaritifera
The European freshwater pearl mussel belongs to the family Margaritiferidae. It favours cool, nutrient-poor, oxygen-rich flowing waters with stable gravelly and sandy beds through which water can circulate freely.
This species is exceptionally long-lived; some individuals survive for well over 100 years. Its natural reproduction, however, depends on very particular environmental conditions.
The glochidia require suitable host fish from the salmon family (Salmonidae), particularly brown trout or Atlantic salmon. Once this stage is complete, juvenile mussels spend several years largely concealed within the riverbed.²
During this early stage they are extremely sensitive to oxygen depletion and the accumulation of fine sediment. If particles washed into the river fill the spaces between the gravel, the necessary exchange of water becomes inadequate.
Intensive farming, nutrient inputs, river engineering and changes to natural river dynamics are among the causes of the species' severe decline. Historical collection for natural pearls has also contributed.
The European freshwater pearl mussel is now considered endangered worldwide and critically endangered in Europe. Extensive conservation and reintroduction programmes aim to protect remaining populations.²
Historically, the species was important as a source of European river pearls. It has virtually no role in contemporary commercial pearl cultivation.
Japanese Biwa Pearl Mussel – Sinohyriopsis schlegelii
The Japanese Biwa pearl mussel was described in older scientific publications as Hyriopsis schlegelii. It belongs to the family Unionidae and is particularly well known for its use in Japanese freshwater pearl cultivation.
During the twentieth century, a significant pearl-farming industry developed in Lake Biwa, Japan's largest freshwater lake. The pearls produced there were valued for their varied natural colours, lustre and often elongated or irregular shapes.
Japanese freshwater pearl production reached its peak during the 1970s. Thereafter, deteriorating water quality, changes to the ecosystem and declining populations of suitable mussels brought about a drastic fall in production.³
Pearl cultivation in Lake Biwa did not, however, cease entirely. Scientific studies confirm that pearls were still being cultivated and harvested there in the twenty-first century. Hybrids of the Japanese Sinohyriopsis schlegelii and the Chinese Sinohyriopsis cumingii are used in some cases.⁴
An important further development took place at Lake Kasumigaura, where more resilient hybrids of the two species were employed. The resulting pearls are known as Kasumiga or Kasumigaura pearls.
Geographical origin matters: the term ‘Biwa pearl’ originally refers to pearls from Japan's Lake Biwa. Freshwater pearls of a similar appearance from other growing regions do not automatically have the same geographical provenance.
Chinese Cockscomb Pearl Mussel – Cristaria plicata
Cristaria plicata also belongs to the family Unionidae and occurs in East Asia.
This mussel played a major part in the historical development of Chinese freshwater pearl cultivation. As early as medieval China, the species was used to coat small religious figures attached to the inside of the shell with nacre.
As Chinese pearl farming expanded in the 1960s and 1970s, Cristaria plicata once again became economically significant.
By inserting small pieces of mantle tissue, numerous non-bead-cultured pearls could develop within a single mussel. Production at that time was largely directed towards high volumes.
Many of these early Chinese cultured pearls were comparatively small and irregularly shaped, often with distinctly ridged or furrowed surfaces.
As cultivation techniques developed, Cristaria plicata was increasingly replaced by other species, particularly Sinohyriopsis cumingii, which made it possible to produce more pearls of greater size, more regular shape and good lustre.⁵
Nevertheless, Cristaria plicata remains an important species in the history of modern freshwater pearl cultivation.
Chinese Triangle Mussel – Sinohyriopsis cumingii
The Chinese triangle mussel, described in older literature as Hyriopsis cumingii, is among the most important species in modern freshwater pearl cultivation.
Its common name reflects the approximately triangular outline of its shell.
Native to East Asia, the species is cultivated principally in China to produce high-quality freshwater cultured pearls.
Its importance is partly due to its ability to produce high-quality nacre under suitable farming conditions. It is used both for non-bead-cultured pearls and for modern methods involving the insertion of a bead nucleus.
Advances in cultivation have resulted in increasingly large, near-round and sometimes strikingly colourful pearls.
Selective breeding is particularly important. For instance, mussels showing particular nacre colours may be chosen as donors of the mantle tissue required for grafting.
Because the grafted mantle tissue participates in forming the pearl sac and hence the pearl's subsequent nacre, its origin can influence the colour and optical properties of the resulting pearl.
Alongside the selection of suitable breeding lines, hybrids between Sinohyriopsis cumingii and Sinohyriopsis schlegelii have also been developed.
These advances established important conditions for the production of large, bead-nucleated freshwater cultured pearls, including products sold under the names Ming or Edison.⁵ ⁶
Chinese Pond Mussel – Sinanodonta woodiana
The Chinese pond mussel is native to East Asia and also belongs to the family Unionidae.
It is notable for its relatively high adaptability to different environmental conditions. In addition to lakes and ponds, it can inhabit slow-flowing waters.
It is substantially more tolerant of varying water and sediment conditions than many sensitive native freshwater mussel species.
Sinanodonta woodiana, frequently referred to as Anodonta woodiana in older publications, has also been used in Chinese pearl cultivation. Historical reports by the Food and Agriculture Organization of the United Nations (FAO) document its rearing alongside Cristaria plicata and Hyriopsis cumingii at Chinese farming facilities.⁷
It does not, however, have the same commercial importance as Sinohyriopsis cumingii in today's production of high-quality freshwater cultured pearls.
Ecologically, this mussel is particularly interesting. It has reached Europe and other parts of the world through the stocking of fish and dispersal of its larvae.
It can reproduce successfully in suitable habitats. Owing to its adaptability and its ability to compete with native mussel species, it is studied as an invasive species beyond its natural distribution.¹
The Importance of Freshwater Mussel Species to Pearl Cultivation
The development of modern freshwater pearl cultivation is closely linked to the selection of suitable mussel species.
Whereas the European freshwater pearl mussel historically supplied mainly natural pearls, commercial cultivation was developed first in Japan and subsequently, above all, in China.
Production gradually shifted from an emphasis on obtaining the greatest possible numbers to more deliberate improvements in pearl quality.
The species selected, the genetic characteristics of farmed mussels, the provenance of grafted mantle tissue and environmental conditions during growth all influence the outcome.
The diversity of today's freshwater cultured pearls therefore reflects not only different cultivation techniques, but also decades of progress in mussel breeding.
Scientific References
1. Douda, K. et al. (2024). Review of the globally invasive freshwater mussels in the genus Sinanodonta Modell, 1945. Hydrobiologia.
https://doi.org/10.1007/s10750-023-05457-3
2. Moorkens, E. A. et al. (2026). Synopsis of the European freshwater mussels: Margaritifera margaritifera (Linnaeus, 1758), the freshwater pearl mussel. Hydrobiologia.
https://doi.org/10.1007/s10750-025-06096-6
3. Abduriyim, A. (2018). Cultured Pearls from Lake Kasumigaura: Production and Gemological Characteristics. Gems & Gemology, vol. 54, No. 2.
4. Nilpetploy, N. & Katsurada, Y. (2021). Unique Non-Bead Cultured Freshwater Pearls from Lake Biwa, Cultured for 14 Years. Gems & Gemology, vol. 57, No. 2.
5. Fiske, D. & Shepherd, J. (2007). Continuity and Change in Chinese Freshwater Pearl Culture. Gems & Gemology, vol. 43, No. 2, pp. 138–145.
6. Zhou, Q., Xu, Y., Xu, D., Hu, J. & Zhao, M. (2026). Policy-Driven Sustainability in China’s Freshwater Pearl Culturing Industry. Gems & Gemology, vol. 62, No. 2.
7. Food and Agriculture Organization of the United Nations (FAO). Freshwater Aquaculture Development in China – Cultured Pearl Production in Fresh Water. Historical technical report.
https://www.fao.org/4/ad016e/ad016e12.htm
Additional taxonomic reference:
MolluscaBase / World Register of Marine Species (WoRMS). Scientific nomenclature and synonyms of the mussel species mentioned.
Marine Bivalves
The most important bivalves used in commercial marine pearl cultivation belong to the genera Pinctada and Pteria. They are found predominantly in tropical and subtropical seas, occupying lagoons, bays, coastal reefs and other suitable marine habitats, depending on the species.
In everyday English, these animals are often called pearl oysters. Zoologically, however, they are not true oysters. True oysters belong to the family Ostreidae, while Pinctada and Pteria belong to different families.
Traditionally, both genera were placed in the family Pteriidae. More recent molecular phylogenetic studies have shown that this classification does not fully reflect their evolutionary relationships.
Accordingly, the current classification used by MolluscaBase and the World Register of Marine Species (WoRMS) places Pinctada in Margaritidae and Pteria in Pteriidae. Both families belong to the superfamily Pterioidea.¹ ²
Like freshwater mussels, marine pearl-producing bivalves feed by filtering water. Their gills collect microscopic food particles, especially phytoplankton and other suspended organic matter.
Their reproductive cycle, however, differs considerably from that of many freshwater mussels.
Marine pearl oysters generally release eggs and sperm into the surrounding water, where fertilisation takes place. The fertilised eggs develop into free-swimming larvae.
These pass through several developmental stages, including the veliger stage. At this point they possess a ciliated structure known as the velum, which assists with movement and feeding.
At the end of the planktonic phase, the larvae seek a suitable surface on which to settle and develop into juvenile bivalves. Many species attach themselves to rocks, coral or other firm substrates by means of byssal threads.³
These molluscs are especially well adapted to producing nacre. The inner surfaces of their shells are lined with nacre, whose colours and optical characteristics vary between species.
Only a relatively small number of species have become commercially important in pearl cultivation.
Akoya Pearl Oyster – Pinctada fucata
The Akoya pearl oyster is one of the best-known species of Pinctada. It is farmed particularly in Japan and China for the production of Akoya pearls.
Older, and some contemporary, gemmological publications frequently use the names Pinctada fucata martensii or Pinctada martensii. In the current WoRMS taxonomic database, these are treated as synonyms of Pinctada fucata.²
Compared with other commercially cultivated marine pearl oysters, this is a relatively small species. Its pearls are correspondingly generally smaller than Tahitian or South Sea pearls.
Akoya cultured pearls commonly measure approximately 6–9 millimetres across. Larger examples are possible but become increasingly uncommon with size.
They are especially well known for their frequently near-spherical shape and pronounced, mirror-like lustre.
Their natural colours include white, cream, yellow and silvery shades, sometimes accompanied by additional hues or overtones. Some commercially sold Akoya pearls undergo treatment after harvesting to alter their colour or appearance.
Cultivation normally involves inserting a spherical nucleus and a small piece of mantle tissue into the oyster. The transplanted epithelial cells develop into a pearl sac, which gradually deposits nacre around the nucleus.
Japanese Akoya cultivation played a decisive part in establishing the modern commercial pearl industry. This mollusc remains economically significant today.⁴
Black-Lipped Pearl Oyster – Pinctada margaritifera
The black-lipped pearl oyster, Pinctada margaritifera, is distributed across much of the tropical Indo-Pacific.
Its name refers to the dark border of the nacreous inner shell, which may display black, grey and greenish colours.
The species is particularly well known for producing Tahitian pearls. Commercial production is concentrated in French Polynesia, especially in the lagoons of the Tuamotu and Gambier Islands.
The term ‘Tahitian pearl’ therefore does not mean that a particular pearl necessarily grew in waters immediately surrounding the island of Tahiti.
The natural colour range is remarkably varied. In addition to dark grey and black, these pearls can display green, blue, violet and brown tones.
Some also have pronounced overtones or striking colour effects described in trade terminology as peacock.
Although commonly referred to as black pearls, genuinely black specimens represent only part of the natural colour range.
Most commercial Tahitian cultured pearls are produced by inserting a spherical nucleus together with a piece of mantle tissue. Under suitable conditions the mollusc forms a nacreous layer around the nucleus; its structure, colour and surface characteristics are influenced during growth.
Non-bead-cultured pearls also occasionally arise in these oysters, sometimes as by-products of cultivation.
Such pearls are of gemmological interest because the internal growth features of natural pearls and non-bead-cultured pearls may partly resemble one another.⁵
South Sea Pearl Oyster – Pinctada maxima
Pinctada maxima is the largest of the commercially important pearl oysters in the genus Pinctada.
Its shells may exceed 30 centimetres in diameter. The size of the mollusc allows particularly large pearls to develop.
Its natural range covers extensive parts of the tropical Indo-Pacific. Important farming regions include the coasts of Australia, Indonesia, the Philippines and Myanmar.
Silver-lipped and gold-lipped forms of Pinctada maxima are distinguished according to the colour of the nacre along the inner shell margin.
Both forms belong to the same species.
The silver-lipped form is particularly associated with white, cream and silvery South Sea pearls. The gold-lipped form is well known for pearls ranging from yellow to intense gold.
The colour of the nacre and the characteristics of the transplanted donor mantle tissue influence the resulting pearls. Nevertheless, the colour of an individual pearl cannot be predicted solely from the external appearance of the host oyster.
South Sea cultured pearls frequently measure around 8–20 millimetres, although individual specimens may be larger.
Alongside their size, fine South Sea pearls are often distinguished by a soft, silky-looking lustre.
Cultivation usually involves a nucleus and a mantle-tissue graft. Because of the oyster's size, comparatively large nuclei can be implanted.
The nacre, however, takes time to grow. Growth periods of two years or more are often required for high-quality South Sea cultured pearls.
During this period the health of the oyster, water temperature, food availability and other environmental factors affect development.
Research on Pinctada maxima has also shown that non-bead-cultured pearls may develop alongside the intended bead-cultured pearls. These are harvested as by-products and sometimes display complex internal growth structures.⁶
Winged Pearl Oyster – Pteria penguin
Pteria penguin is a marine pearl-producing bivalve found particularly in tropical and subtropical parts of the Indo-Pacific.
Unlike the more rounded shells of many Pinctada species, it has a strikingly asymmetric, wing-like shell shape.
Its shells can grow to a considerable size and may show a wide range of nacre colours internally.
The species is particularly important in the cultivation of mabé pearls.
In this process, a hemispherical or otherwise shaped object is attached to the inner surface of the shell.
Over time the mantle deposits nacre over the inserted object, producing a raised nacreous formation fused to the shell.
After harvesting, the grown portion is separated from the shell. In the production of a typical commercial mabé pearl, the original form is removed, the resulting cavity is filled and a suitable backing is attached.
A finished mabé therefore has a different internal construction from that of a pearl grown completely within a free pearl sac.
The term mabé is not restricted to pearls from Pteria penguin. Similar cultivation methods are used with other pearl-producing molluscs.
Research on Pteria penguin has shown that oyster size, the duration of cultivation and growing conditions can all influence the development of mabé pearls.⁷ ⁸
Rainbow-Lipped Pearl Oyster – Pteria sterna
Pteria sterna occurs in the eastern Pacific, including the Mexican Pacific coast and the Gulf of California.
The English name ‘rainbow-lipped pearl oyster’ refers to the many-coloured nacre inside its shell, which can show violet, green, blue and other iridescent hues.
This species is especially important in the cultivation of Cortez pearls.
They are farmed in the Gulf of California, also known as the Sea of Cortez.
Their colours can differ markedly from those of other marine cultured pearls.
Alongside grey and brown body colours, they may display pronounced green, blue, violet and reddish overtones. Some examples have a particularly striking metallic-looking lustre.
Whereas Pteria penguin is mainly associated with mabé cultivation, Pteria sterna can also produce complete bead-cultured pearls.
Scientific studies have shown that the natural colour of these pearls can be investigated using their spectroscopic characteristics and distinctive fluorescence responses.
Compared with major international production regions, Cortez pearl cultivation operates on a much smaller scale. Nevertheless, it illustrates how a regionally occurring species can be used to produce cultured pearls with an individual character.⁹
Mazatlán Pearl Oyster – Pinctada mazatlanica
Another pearl oyster native to the eastern Pacific is Pinctada mazatlanica.
It is found particularly along the Pacific coast of Central America and in the Gulf of California. Owing to the dark margin of its nacre, it too is sometimes called a black-lipped pearl oyster.
Historically, this species was collected on the Mexican Pacific coast for its natural pearls and mother-of-pearl.
It also played a part in the development of modern pearl cultivation in the Gulf of California.
Cultivation trials investigated both Pinctada mazatlanica and Pteria sterna. However, Pteria sterna became the principal species used for commercial bead-cultured Cortez pearls.
The two are zoologically distinct despite sharing some marine habitats and both being capable of producing natural pearls.
It would therefore be incorrect to attribute all pearls originating in the Gulf of California to a single species.⁹
Gulf Pearl Oyster – Pinctada radiata
Pinctada radiata is another pearl-producing bivalve, known especially for its historical importance in natural pearl fishing.
It occurs in the Persian Gulf, the Red Sea and neighbouring marine regions.
For centuries this species played a significant role in traditional pearl diving. The waters around Bahrain and along the Arabian Gulf coast were especially renowned for natural pearls.
Compared with the larger Pinctada maxima and Pinctada margaritifera, Pinctada radiata remains relatively small.
Its natural pearls are therefore generally small, although they may show strong lustre and white, cream or yellowish colours.
Modern gemmological examinations show that even tiny natural pearls from this species can have complex internal growth structures.
These can be investigated by X-ray microradiography and X-ray computed tomography.
Pinctada radiata is much less important to present-day global cultured-pearl production than the principal commercial Pinctada species.
Its historical significance as a source of natural pearls nevertheless remains considerable.¹⁰
Baltic Sea Mussels – Species of Mytilus
Pearl formation is by no means restricted to the marine bivalves traditionally used for cultivation. Even mussels of the genus Mytilus, which occur in the German Baltic Sea, can produce pearls.
These animals belong to the family Mytilidae, not to the pearl-oyster families Margaritidae or Pteriidae. The Baltic populations include species within the Mytilus complex, notably Mytilus edulis, Mytilus trossulus and hybrids. Their precise taxonomic identification is not always straightforward.¹¹
The ability of these mussels to form pearls has been documented scientifically. A Norwegian study published in 2018 found nearly 2,000 small pearls in a sample of 280 Mytilus mussels. Numbers varied greatly between individuals. These findings relate to the Norwegian coast and cannot be applied directly to Baltic Sea populations.¹²
One possible trigger is parasitic infection. In a study published in 2023 on Mytilus edulis from northern Norway, researchers detected DNA from the parasitic trematode Gymnophallus bursicola inside pearls. This confirmed a direct link between parasitic infection and pearl formation in the mussels examined.¹³
The pearls produced by mussels are often small and irregular. Baltic Mytilus populations are not commercially cultivated for jewellery pearls. They nevertheless demonstrate that the capacity to form pearls also occurs in marine bivalves outside the traditional pearl-cultivation industry.
The Importance of Marine Pearl Oysters to Cultivation
Modern marine pearl cultivation is concentrated on a small number of species whose biology makes the deliberate introduction of nuclei and mantle tissue possible.
The species of greatest commercial significance are Pinctada fucata, Pinctada margaritifera and Pinctada maxima.
Other species are important in specialised cultivation, regional production or the historical harvesting of natural pearls.
Differences between species strongly influence the sizes, shapes, colours and optical characteristics that can develop in their pearls.
Considerable variation also exists within an individual species. Genetics, the selection of donor mantle tissue, the nuclei used and environmental conditions during growth interact to influence the outcome.
The biological origin of a pearl is therefore an important part of its identity.
Akoya, Tahitian and South Sea pearls differ not merely in where they are produced or how they look, but fundamentally in the mollusc species within which they grow.
Understanding these connections provides an essential foundation for studying the different pearl types and their methods of cultivation.
Scientific References
1. Tëmkin, I. (2010). Molecular phylogeny of pearl oysters and their relatives (Mollusca, Bivalvia, Pterioidea). BMC Evolutionary Biology, 10, article 342.
https://doi.org/10.1186/1471-2148-10-342
2. MolluscaBase / World Register of Marine Species (WoRMS). Taxonomic classification and synonyms of the genera Pinctada und Pteria. Continuously updated scientific database.
https://www.marinespecies.org/aphia.php?p=taxlist&tName=Pinctada
https://www.marinespecies.org/aphia.php?p=taxlist&tName=Pteria
3. Destanque, T. et al. (2024). Substantial gene expression shifts during larval transitions in the pearl oyster Pinctada margaritifera. Journal of Experimental Zoology Part B: Molecular and Developmental Evolution.
https://doi.org/10.1002/jez.b.23243
4. Homkrajae, A. (2024). Remarkably Large Akoya Bead Cultured Pearls. Gems & Gemology, vol. 60, No. 2.
https://www.gia.edu/gems-gemology/summer-2024-gemnews-large-akoya-bead-cultured-pearls
5. Nilpetploy, N., Lawanwong, K. & Kessrapong, P. (2018). Non-Bead-Cultured Pearls from Pinctada margaritifera. GIA Research.
https://www.gia.edu/ongoing-research/non-bead-cultured-pearls-from-pinctada-margaritifera
6. Homkrajae, A. et al. (2021). Internal Structures of Known Pinctada maxima Pearls: Cultured Pearls from Operated Marine Mollusks. Gems & Gemology, vol. 57, No. 3.
https://www.gia.edu/gems-gemology/fall-2021-internal-structures-pinctada-maxima-pearls
7. Kanjanachatree, K. et al. (2019). Effects of Mollusk Size on Growth and Color of Cultured Half-Pearls from Phuket, Thailand. Gems & Gemology, vol. 55, No. 3.
https://www.gia.edu/gems-gemology/fall-2019-half-pearls-from-phuket-thailand
8. Leblan, S. et al. (2021). Mabe Cultivation in Mayotte. Gems & Gemology, vol. 57, No. 3.
https://www.gia.edu/gems-gemology/fall-2021-gemnews-mabe-cultivation-mayotte
9. Kiefert, L., McLaurin Moreno, D., Arizmendi, E., Hänni, H. A. & Elen, S. (2004). Cultured Pearls from the Gulf of California, Mexico. Gems & Gemology, vol. 40, No. 1, pp. 26–38.
https://origin.prod.gia.edu/gems-gemology/spring-2004-cultured-pearls-gulf-california-mexico-kiefert
10. Atchalak, R., Lawanwong, K., Yazawa, E. & Al-Alawi, A. (2023). An Unusual Metallic Core in a Natural Pinctada radiata Pearl from Kuwait. Gems & Gemology, vol. 59, No. 2.
https://origin.prod.author.gia.edu/gems-gemology/summer-2023-gemnews-metallic-core-pinctada-radiata
11. Umweltbundesamt (2024). Gewässertyp des Jahres 2024 – Flaches Küstengewässer der Ostsee. Section ‘Miesmuschel (Mytilus-Komplex)’ (mussels of the Mytilus complex).
12. Bråte, I. L. N., Buenaventura, N. T. & Lusher, A. (2018). Occurrence of pearls in mussels (Mytilus spp.) from the Norwegian coast. NIVA Report 7308-2018, Norwegian Institute for Water Research.
13. Benito, D. et al. (2023). Molecular confirmation of pearl formation in arctic mussels (Mytilus edulis) caused by Gymnophallus bursicola (Odhner 1900) metacercariae. Parasitology, 150(11), 1015–1021.
https://doi.org/10.1017/S0031182023000860
Further specialist literature:
Gervis, M. H. & Sims, N. A. (1992). Biology and Culture of Pearl Oysters (Bivalvia: Pteriidae). ICLARM Studies and Reviews 21. Overview of the biology and cultivation of the principal marine pearl oysters.
https://ntrl.ntis.gov/NTRL/dashboard/searchResults/titleDetail/PB94191558.xhtml
How Pearls Form
Pearls form through a biological process in which specialised cells in a mollusc secrete mineral and organic substances. This process is closely related to the formation of the mollusc's shell.
The fundamental mechanisms of pearl formation are relatively well understood. In particular, scientists know which cells are responsible for producing nacre and how the characteristic layered structure of a pearl develops.
What is less clearly understood is why a natural pearl begins to form in a wild mollusc in the first place.
For a long time, it was assumed that a grain of sand entering the animal triggered the process. According to this familiar account, the mollusc protects itself from an irritating foreign body by coating it with nacre.
This explanation is too simplistic and is no longer regarded as a generally valid account of natural pearl formation.
The Importance of Mantle Tissue
To understand how a pearl develops, we must first consider the anatomy of a bivalve.
Its soft body is surrounded by a tissue layer known as the mantle (pallium). Among other functions, the mantle is responsible for the formation and growth of the shell.
Its outer surface is covered by a layer of specialised cells called the mantle epithelium.
These epithelial cells produce and transport the substances from which the calcareous shell structures are built. In nacre-producing molluscs, they are also responsible for making nacre.
The required mineral constituents are secreted together with organic molecules in a biologically controlled process.
Importantly, the animal is not simply precipitating dissolved limestone from the surrounding water. Its cells regulate the supply of the constituent substances and the organisation of the resulting crystal structures.
This process is known as biomineralisation.¹
The Pearl Sac – the Organ That Actually Produces a Pearl
The formation of a free nacreous pearl within the soft body requires a specialised cellular structure: the pearl sac.
The pearl sac is an enclosed tissue structure lined with epithelial cells. These cells can secrete mineral and organic constituents towards the interior.
Under normal circumstances, the mantle epithelium produces shell material on the inner surface of the shell.
If suitable epithelial cells become displaced into deeper tissue, however, they may under certain conditions establish a separate cell layer that closes to form a pearl sac.
The sac then functions, in a sense, as a small shell-forming organ separated from the original mantle.
The cells lining its inner surface secrete the material from which the pearl develops.
The pearl therefore grows within the pearl sac, while the sac itself remains a living cellular structure connected to the surrounding tissues.
A number of scientific investigations have confirmed the essential role of mantle epithelial cells.
Particularly revealing are experiments in which isolated mantle epithelial cells were cultured outside the living animal. Researchers demonstrated that these cells could produce nacre-like mineral deposits even under artificial cell-culture conditions.²
How Does a Natural Pearl Begin to Form?
In natural pearls, the pearl sac develops without deliberate human intervention.
One possible starting point is an injury to the mantle. Epithelial cells may then become displaced from their original position into deeper connective tissue.
There they may multiply and form a closed cellular structure that develops into a pearl sac.
Possible causes of such injuries include parasites, other invading organisms and mechanical damage. Other processes, including changes or abnormal development in epithelial cells, have also been discussed as potential triggers.³
The possible involvement of parasites is not merely theoretical.
A study published in 2016 on the marine mussel Aulacomya atra demonstrated an association between infestation by boring polychaete worms and pearl formation. The pearls examined contained, among other things, remains of the parasites concerned.⁴
This does not, however, mean that all natural pearls develop as a result of parasitic infection.
Examinations of natural pearls reveal a wide range of internal growth structures.
In a study published in 2021, the Gemological Institute of America examined 774 natural pearls recovered directly from wild Pinctada maxima oysters.
Researchers observed different internal structures, including compact mineral zones, organic growth zones, cavities and linear features.
Only a few specimens contained features suggestive of marine organisms enclosed as possible initiators of pearl formation.³
The natural causes of pearl-sac formation cannot therefore be reconstructed in every individual case.
Why the Grain-of-Sand Explanation Falls Short
The familiar idea that a grain of sand enters a mollusc and is gradually covered in nacre does not adequately describe the biology involved.
Many bivalves live in close contact with sand, mud or other sediment. They have mechanisms for moving particles that enter the mantle cavity and for expelling unwanted material.
Consequently, an ordinary grain of sand does not automatically cause a pearl to form.
For a free nacreous pearl to grow within soft tissue, the crucial event is the establishment of a functioning pearl sac from suitable epithelial cells.
A foreign object may contribute under certain circumstances, for example by causing tissue damage, but it is not an essential prerequisite for pearl formation.
Nor must every natural pearl contain a grain of sand or another clearly identifiable object at its centre.
The formation of a natural pearl should therefore not be understood simply as the encapsulation of an irritating grain of sand, but as a biological process involving specialised cells of the mollusc.
How a Cultured Pearl Is Produced
Modern pearl cultivation deliberately uses the mantle's ability to form a pearl sac and deposit nacre within it.
The basic biological mechanism does not differ from natural pearl formation.
The principal distinction is that, in a cultured pearl, pearl-sac development is initiated by human intervention.
Different procedures are used depending on the mollusc species and the type of pearl being produced.
Bead-Cultured Pearls
In conventional Akoya, Tahitian and South Sea pearl cultivation, a spherical bead nucleus is inserted into suitable soft tissue together with a small piece of mantle tissue.
The nucleus is usually made from worked mollusc shell material.
The grafted mantle tissue, often called saibo, comes from a donor mollusc.
Following the operation, epithelial cells from the graft begin to spread and multiply.
They surround the nucleus, forming a closed pearl sac.
Only through the activity of these living cells does the implanted bead gradually acquire its coating of biologically produced material.
Research on Pinctada margaritifera indicates how quickly the initial pearl sac can develop.
In a study published in 2015, the implanted nucleus was fully enclosed by a pearl sac just twelve days after the operation. The first organic layer had already begun to be deposited.
After approximately three months, the experimental nuclei were completely covered with nacre.⁵
These observations apply to the conditions studied and should not be generalised to every mollusc species or cultivation method.
A considerably longer period is usually needed before a cultured pearl reaches a commercially suitable stage for harvesting.
Non-Bead-Cultured Pearls
Traditional non-bead freshwater pearl cultivation does not involve inserting a preformed spherical nucleus.
Instead, small pieces of suitable mantle tissue are transplanted into the host mussel.
Pearl sacs develop from the grafted epithelial cells, and the secretion of mineral and organic material begins.
The resulting pearl therefore has no large, artificially inserted shell bead at its centre.
Tissue remnants or organic matter may initially remain at the centre, around which subsequent layers develop.
As it grows, the pearl comes to consist predominantly of material deposited by the mollusc itself.
The absence of an implanted bead does not, however, make such a pearl a natural pearl.
Non-bead-cultured pearls are still the result of deliberate human intervention.
Non-bead-cultured pearls may also arise unintentionally during marine pearl cultivation. One example occurs when the host expels an implanted bead after the pearl sac has already formed and the sac continues depositing mineral material.
Such pearls are often described in the trade as keshi pearls.⁶
How Does a Pearl Grow?
Once the pearl sac has formed, the development of the pearl itself begins.
Its epithelial cells secrete a complex mixture of mineral constituents and organic molecules.
In traditional nacreous pearls, the mineral component consists mainly of aragonite, a crystalline form of calcium carbonate (CaCO₃).
Aragonite grows in minute, flat platelets, arranged in successive layers separated by thin organic films.
This produces the characteristic structure of nacre.
The organic constituents perform essential functions, influencing the formation, arrangement and growth of the mineral crystals.
Deposition is not perfectly uniform.
Biological rhythms, changing environmental conditions and variations in the activity of the cells involved can all affect growth.
A materials-science study published in 2021 found that nacre layers can develop an exceptionally orderly overall structure despite local irregularities.
The researchers observed mechanisms through which some irregularities are partly compensated for as growth proceeds.⁷
This layered construction is a fundamental condition for nacre's distinctive mechanical and optical properties.
It does not, however, fully explain why pearls may differ so markedly in shape, colour, lustre and surface texture.
These characteristics depend partly on the mollusc species, the biological properties of the pearl-producing cells and the conditions prevailing during growth.
Not All Pearls Have Nacre
The layered arrangement of aragonite platelets described above is characteristic of traditional nacreous pearls.
Not every naturally occurring pearl, however, has this structure.
Certain gastropods and some bivalves form calcareous pearls whose mineral components are arranged differently.
So-called non-nacreous pearls may, for example, contain fibrous or intersecting crystalline structures.
Well-known examples are conch and melo pearls, which can display an unusual flame-like optical effect.
This arises from the interaction of light with the different arrangement of their mineral crystals.
Some non-nacreous pearls also consist largely of calcite rather than aragonite.⁸
These variations show that molluscs can use their ability to control calcium carbonate formation in several different ways.
Free Pearls and Shell-Attached Formations
Not every calcareous, pearl-like formation in a mollusc grows freely within its soft tissues.
A fully formed free pearl develops inside a pearl sac and remains separate from the shell.
Some pearls, however, become attached to the inner shell surface as they grow. These are known as blister pearls.
A natural blister pearl may arise when a pearl initially formed freely within soft tissue comes into contact with the shell and subsequently becomes joined to it by further mineral deposition.
They should be distinguished from shell blisters, which originate directly at the inner shell surface, for example when a foreign object becomes trapped between the mantle and the shell and is subsequently covered with shell material.
Although the two formations may appear similar externally, their development and internal structure differ.
Distinguishing a blister pearl from a shell blister may therefore require an examination of its internal features.⁹
Deliberate production of shell-attached nacreous formations is also used in pearl cultivation, notably in the manufacture of mabé pearls.
The Biological Basis of All Pearls
Whether a pearl forms naturally or is cultivated, its growth depends on living molluscs' ability to produce mineral structures through biological processes.
Cultivation methods primarily alter the conditions under which this process is initiated.
The deposition of mineral and organic layers remains the work of the living organism.
A cultured pearl is therefore not an artificially manufactured object in the usual sense, but the outcome of biological growth.
Its shape, surface and optical characteristics reflect the complex processes that occurred within the animal as it developed.
Scientific References
1. Wada, K. (1975). Biomineralogy and Pearl Culture – 2. Journal of the Gemmological Society of Japan, 2(1), pp. 3–10.
https://doi.org/10.14915/gsjapan.2.1_3
2. Jayasankar, V., Vasudevan, S. R., Poulose, S. C. & Divipala, I. (2018). Nacre formation by epithelial cell cultures from mantle of the black-lip pearl oyster, Pinctada margaritifera. In Vitro Cellular & Developmental Biology – Animal, 54, pp. 477–485.
https://doi.org/10.1007/s11626-018-0269-z
3. Homkrajae, A. et al. (2021). Internal Structures of Known Pinctada maxima Pearls: Natural Pearls from Wild Marine Mollusks. Gems & Gemology, 57(1).
4. Diez, M. E., Vázquez, N. & Cremonte, F. (2016). Pearls in the ribbed mussel Aulacomya atra caused by polydorin polychaetes (Spionidae) infestation. Journal of Invertebrate Pathology, 140, pp. 42–45.
https://doi.org/10.1016/j.jip.2016.08.011
5. Kishore, P. & Southgate, P. C. (2015). Development and function of pearl-sacs grown from regenerated mantle graft tissue in the black-lip pearl oyster, Pinctada margaritifera. Fish & Shellfish Immunology, 45(2), pp. 567–573.
https://doi.org/10.1016/j.fsi.2015.05.008
6. Nilpetploy, N., Lawanwong, K. & Kessrapong, P. (2018). Non-Bead-Cultured Pearls from Pinctada margaritifera. Gemological Institute of America, Research News.
https://www.gia.edu/gia-news-research/non-bead-cultured-pearls-from-pinctada-margaritifera
7. Gim, J. et al. (2021). The mesoscale order of nacreous pearls. Proceedings of the National Academy of Sciences (PNAS), 118(42), e2107477118.
https://doi.org/10.1073/pnas.2107477118
8. Gemological Institute of America (2024). Analysis of Gemstones at GIA Laboratories. Gems & Gemology, Winter 2024. Section ‘Pearls’.
https://www.gia.edu/gems-gemology/winter-2024-gemstone-analysis
9. Lawanwong, K., Nilpetploy, N., Manustrong, A. & Homkrajae, A. Natural Shell Blisters and Blister Pearls: What's the Difference? Gemological Institute of America, Research News.
https://www.gia.edu/gia-news-research/natural-shell-blisters-and-blister-pearls
Further scientific literature:
Stevens, K. et al. (2020). Pearl formation in an Early Cretaceous belemnite. PalZ, 94, pp. 481–486.
https://doi.org/10.1007/s12542-020-00521-y
This palaeontological study examines a fossil pearl and discusses the significance of displaced mantle epithelial cells for pearl-sac formation.
Chemical Composition and Properties of Pearls
Pearls are remarkable natural materials. They consist mainly of calcium carbonate, a chemical compound found widely in nature, including in limestone, chalk and many mollusc shells.
Nevertheless, pearls differ significantly from ordinary limestone in their properties.
The reason lies less in their chemical composition than in the special arrangement of their mineral and organic components.
Pearl-producing molluscs are able to combine these substances through biological processes into a complex, finely ordered structure.
The resulting natural composite material has mechanical and optical properties that have been studied scientifically for decades.
Calcium Carbonate – the Principal Mineral Constituent
The chief mineral constituent of most pearls is calcium carbonate (CaCO₃).
The compound consists of positively charged calcium ions (Ca²⁺) and negatively charged carbonate ions (CO₃²⁻).
Calcium carbonate occurs in three crystalline modifications in nature:
- Calcite: the thermodynamically most stable crystalline form under ordinary ambient conditions. Calcite has a trigonal crystal structure and is the principal component of many limestones.
- Aragonite: another crystalline form with an orthorhombic crystal structure. Its chemical composition is identical to calcite's, but the atoms are arranged differently.
- Vaterite: a third, comparatively unstable crystalline form of calcium carbonate, which under suitable conditions can transform into more stable forms.
Different crystal structures of the same chemical substance are known as polymorphs.
Although their chemical constituents are identical, the different atomic arrangements can give them different physical properties.
Aragonite forms the predominant mineral component of traditional nacreous pearls.
Calcite can also occur in particular pearl structures. Vaterite is considerably rarer, although it has been identified in certain freshwater cultured pearls.
Investigations by the Gemological Institute of America have shown, for example, that vaterite may occur as irregular whitish areas on the surfaces of freshwater cultured pearls. Raman spectroscopy allowed researchers to identify the differing crystal structure.¹
Not every pearl, however, has the same mineral composition.
Whereas nacreous pearls contain predominantly aragonite, certain non-nacreous pearls may contain a substantial proportion of calcite or consist chiefly of it.
Composition thus also depends on the mollusc species and the biological formation process.
Nacre – a Natural Composite Material
The inner surface of many pearl-producing bivalve shells is lined with a lustrous layer called nacre, commonly known as mother-of-pearl.
Nacre is not a single homogeneous mineral, but a biologically produced composite of mineral and organic components.
In many investigated nacre structures, approximately 95 per cent of the mass is aragonite and about 5 per cent organic material. These are typical approximate figures for nacre rather than an immutable composition applying to every pearl.²
The organic components consist mainly of proteins, glycoproteins and polysaccharides. They also include chitin, a structural polysaccharide found in many invertebrates.
During biomineralisation, the mineral and organic constituents are assembled in a precisely controlled spatial arrangement.
The resulting material therefore has properties that cannot be explained by its individual chemical substances alone.
Its internal architecture is the essential distinguishing feature.
The Microscopic Structure of Nacre
Under an electron microscope, nacre displays a characteristic layered arrangement.
Its mineral portion consists of extremely small, predominantly flat aragonite crystals.
Depending on the mollusc species and growth conditions, these platelets are often only a few tenths of a micrometre thick, although they may extend several micrometres laterally.
One micrometre (µm) is one thousandth of a millimetre.
The individual aragonite platelets are arranged in successive layers, with very thin organic regions between them.
Materials scientists often compare this structure to a brick wall.
The hard aragonite platelets represent the bricks, while the organic matrix serves rather like the material connecting them.
The relationship is, however, considerably more complex than ordinary mortar.
The platelets are not simply loosely glued together. Mineral connections, microscopic interlocking and organic molecular structures may link them.
The aragonite platelets themselves also have a finer internal organisation extending down to the nanometre scale.
Scientific investigations demonstrate that this hierarchical structure is responsible for nacre's unusual mechanical properties.²
In a pearl, successive nacre layers broadly follow the surface of the growing body, forming an approximately concentric structure.
Local differences in layer thickness, arrangement and crystal orientation may nevertheless occur as growth proceeds.
These differences can also influence the eventual appearance of the pearl's surface.
The Organic Matrix – More Than a Binding Agent
Older scientific and gemmological literature often uses conchiolin as a collective term for the organic constituents of nacre.
It does not, however, designate one chemically defined substance.
Rather, the term encompasses different organic components, particularly protein-rich structures involved in the formation of shells and nacre.
The organic matrix serves several essential functions.
It provides a structural framework within which the mineral components can be organised.
Certain proteins influence the formation of new crystals, their rate of growth and their spatial orientation.
Other organic components help maintain the connections between mineral platelets and absorb mechanical stresses.
The formation of nacre is therefore not a random crystallisation process.
Biologically controlled secretion affects the developing material on several scales.
Recent research also suggests that some calcium carbonate initially occurs during biomineralisation as an amorphous, not yet crystalline precursor.
This phase, called amorphous calcium carbonate (ACC), can subsequently transform into crystalline aragonite.
A study published in 2023 on the nacre layer of the Mediterranean mussel (Mytilus galloprovincialis) demonstrated that this transformation can proceed through local dissolution and recrystallisation within minute mineral regions.³
This highlights the complexity of the process that produces a material which, at first sight, appears to be little more than calcium carbonate.
The precise mechanisms may, however, differ between mollusc species.
Why Nacre Is Mechanically Tough
Pure aragonite is a relatively brittle mineral.
When an aragonite crystal is subjected to excessive mechanical stress, a crack may propagate through it and cause fracture.
Nacre, by contrast, offers remarkable resistance to the propagation of cracks.
This results from combining hard aragonite platelets with the organic structures between them.
When a crack reaches the interface between platelets, it may be deflected, forcing it to follow a longer and more complicated path through the material.
Individual platelets can also move very slightly relative to one another under mechanical loading.
The organic connections between layers stretch and absorb some of the mechanical energy.
Together these mechanisms hinder the spread of a crack.
A material's resistance to the propagation of cracks is called fracture toughness.
Materials-science studies show that the fracture toughness of nacre can be substantially higher than that of pure aragonite; depending on the structure and measurement method, several-fold differences have been reported.²
This property must not be confused with hardness.
A material can have relatively low surface hardness while still showing considerable resistance to complete fracture.
Nacre provides a compelling example of that distinction.
The Hardness of a Pearl
Gemstones and minerals are frequently described using the Mohs scale of hardness.
The scale runs from 1 for talc to 10 for diamond and indicates how well a substance resists scratching by another material.
The mineral aragonite has a Mohs hardness of approximately 3.5–4.
Pearls are somewhat different because their surfaces do not consist of single, homogeneous aragonite crystals.
Organic components, crystal boundaries and the overall composite architecture influence their mechanical properties.
Gemmological references commonly assign pearls a Mohs hardness of approximately 2.5–3.⁴
Pearls are therefore comparatively soft jewellery materials.
Contact with harder gemstones, metal edges or mineral dust can scratch them.
Even apparently soft cleaning cloths can cause damage when hard dust or dirt particles are trapped in the fabric.
The mechanical toughness of nacre should not be taken to mean that pearl surfaces resist abrasion particularly well.
Why Pearls Shine – the Origin of Lustre
The characteristic sheen of a pearl is called lustre.
It is among the most important optical properties of pearls and one of the central criteria used to assess their quality.
Lustre results from the interaction of several physical processes.
When light reaches a pearl, some is reflected directly from the surface.
Another portion penetrates the outer nacre layers.
Within these layers, light is reflected, refracted and scattered at numerous boundaries between the aragonite platelets and the organic films.
Some of this light subsequently emerges from the pearl again.
The visible appearance therefore arises from a combination of light reflected at the surface and light returning from structures beneath it.
A study published in Scientific Reports in 2021 developed an optical model that considers these processes together.
The researchers showed that internal light scattering and the combination of surface-reflected light with light travelling through the nacre layers are particularly relevant to the appearance of pearls.⁵
On a pearl with strong lustre, reflections appear bright, distinct and relatively sharply defined.
On a pearl with weak lustre, they appear more diffuse and less contrasting.
Lustre depends partly on the quality of the outermost nacre layers, the arrangement of the crystal platelets and the surface structure.
The overall thickness of the nacre is not the only factor.
The microscopic quality and arrangement of the most recently deposited layers may have a considerable influence.
Research on Pinctada margaritifera, for example, has shown that lower water temperatures during the final stage of pearl growth may produce thinner aragonite platelets.
Under the conditions investigated, this was associated with better lustre and fewer surface defects.⁶
Light Interference – the Origin of Iridescence
Besides lustre, pearls can display other optical phenomena.
One of the most intriguing is orient, a multicoloured, iridescent effect that can vary with illumination and viewing angle.
One important physical explanation is interference of light.
Light has wave-like properties.
When light waves meet, they can reinforce or weaken one another, depending on their relative phases.
This process is called interference.
Individual nacre layers have thicknesses of an order comparable to the wavelengths of visible light.
Visible wavelengths extend approximately from 380 to 780 nanometres.
A nanometre is one millionth of a millimetre.
When light is reflected at different internal boundaries in nacre, the returning waves can interfere.
Certain wavelengths may consequently be reflected more strongly, while others are weakened.
The thickness and arrangement of the nacre layers can therefore produce different colour impressions.
This phenomenon is known as structural colour.
A structural colour arises not from a pigment, but from the physical interaction between light and a finely organised material structure.
Much of the iridescence of mother-of-pearl is based on this principle.
Related effects can also be observed in pearls.⁵
Lustre, Overtone and Orient
Three terms should be distinguished when describing how a pearl looks.
Lustre primarily describes the intensity, brightness and sharpness of its visible reflections.
Overtone refers to a secondary, often translucent-looking colour perceived over the basic bodycolour of a pearl.
A white pearl, for example, may show a pink or greenish overtone.
Orient refers to an iridescent play of several colours visible on or just beneath the surface.
A pearl with excellent lustre does not necessarily have pronounced orient.
Likewise, a pearl can exhibit unusual optical colour effects without displaying uniformly strong lustre across its entire surface.
The three phenomena are related to nacre's optical properties, but they are not synonymous.⁷
The Natural Colours of Pearls
Pearl colour results from a complex interaction between biological, chemical and physical factors.
A distinction must be made between basic bodycolour and additional optical effects such as overtone and orient.
Bodycolour is influenced partly by natural pigments and other colour-producing organic constituents.
Scientific studies identify melanins and carotenoids, for example, among the biologically important pigment groups that can contribute to colour in certain pearl types.
The organic matrix and the presence of particular metal ions may also affect colour.
Which mechanisms dominate depends on the species.
Genetic characteristics of the mollusc, and particularly the biological properties of the cells forming the pearl sac, also play a significant part.
In graft-based cultivation, choosing donor mantle tissue can therefore influence the pearl's eventual colour.
Environmental conditions during growth can also have an effect. It is not, however, possible simply to assign particular pearl colours to a single water temperature or type of food.
The biological mechanisms of colour production remain an active field of research and are not yet fully understood.⁸
When a pearl is viewed, bodycolour, crystal-structure-related optical effects and surface reflections overlap.
The same pearl may therefore appear different under different lighting conditions.
Trace Elements – Chemical Clues to Origin
In addition to calcium carbonate and organic matter, pearls contain small amounts of other chemical elements.
These include strontium, magnesium and manganese.
Their concentrations may be influenced by the species and its environment.
Strontium and manganese are particularly useful in gemmological analysis.
Freshwater pearls often contain more manganese and less strontium than marine pearls.
For marine pearls, the opposite pattern is commonly observed.
Such differences can provide evidence as to whether a pearl grew in a freshwater or marine environment.
X-ray fluorescence analysis (XRF) is one method used for this purpose.
The sample's atoms are excited by X-rays and subsequently emit characteristic radiation, from which the presence of particular chemical elements can be inferred.
The technique can often be applied without destroying the sample.
Results must nevertheless be interpreted alongside other gemmological findings.
Chemical analysis alone cannot always identify the species or geographic origin of an individual pearl with certainty.⁹
Water as a Component of Pearls
Alongside their mineral and organic constituents, pearls also contain water.
Older gemmological literature reports water contents of approximately 2–4 per cent for certain pearls.
These figures should not be treated as fixed values for every type of pearl.
Actual water content can depend on biological structure, the material examined and the analytical technique used.
Water may occur in different forms within the organic-mineral structure.
Some is associated with organic molecules or interfaces between mineral constituents.
It can consequently influence the mechanical properties of the organic matrix.
Studies of nacre show that its response to mechanical loading can depend partly on its moisture condition.²
This does not mean that water molecules are principally responsible for optical lustre.
Lustre arises mainly from the surface, the mineral crystal structure and the way light travels through the nacre layers.
Nevertheless, substantial changes in moisture condition may indirectly affect how a pearl looks.
Ageing and Dehydration of Pearls
Although pearls contain relatively stable minerals, they can change over time.
Both chemical and physical influences contribute.
Prolonged exposure to high temperatures, large temperature fluctuations and very dry conditions is particularly undesirable.
Under such conditions, water loss and changes in the organic matrix may occur.
These processes can affect mechanical stability and, in unfavourable circumstances, lead to fine cracks, discolouration or deterioration of optical quality.
Long-term exposure to intense ultraviolet radiation may also promote changes in some organic constituents.
Pearl ageing cannot therefore be reduced to one chemical process.
In particular, it would be too simplistic to attribute every loss of lustre exclusively to water loss.
Surface alteration, chemical reactions, mechanical wear or earlier treatments may also play a part.
A study presented to the Gemmological Society of Japan in 2026 demonstrates that these processes are still being investigated. It examined the effects of acids, alkalis, temperature, humidity and light on pearl constituents.¹⁰
Existing cracks or chemically damaged surfaces cannot simply be repaired by placing a pearl in water.
The occasional advice to restore aged pearls by prolonged soaking is therefore not a scientifically established care method.
Careful storage may help avoid damage, but cannot necessarily reverse deterioration that has already occurred.
Chemical Sensitivity to Acids
Because pearls consist predominantly of calcium carbonate, they are sensitive to acids.
Calcium carbonate is attacked by acids, which may dissolve calcium ions and release carbon dioxide.
A simplified chemical equation is:
CaCO₃ + 2 H⁺ → Ca²⁺ + CO₂ + H₂O
This reaction explains why acidic substances can damage a pearl's surface.
Even weak acids may attack calcium carbonate if they remain in contact with it long enough.
Acidic cleaning agents, cosmetics and certain components of human perspiration are particularly relevant to pearl jewellery.
The degree of damage depends on the acid involved, its concentration, the length of exposure and the properties of the pearl's surface.
Brief contact with a very weak acid does not necessarily result in immediately visible damage.
Repeated or prolonged exposure, however, can alter the surface and impair lustre.
Strongly alkaline cleaning agents are also unsuitable.
Here, the mineral component is not the only concern: some alkaline substances can attack the organic constituents of nacre.
Pearls should therefore generally be protected from aggressive chemicals.¹¹
Pearl Care Based on Materials Science
The chemical and physical properties of nacre explain why pearls require different care from many harder gemstones.
Their relatively low surface hardness makes them vulnerable to abrasion.
The organic components and mineral crystal structure can be damaged by unsuitable chemicals, excessive heat and poor storage conditions.
After wearing pearls, it is advisable to wipe them gently with a clean, exceptionally soft cloth.
This removes superficial residues of skin oils, perspiration and other contaminants.
When pearls are more heavily soiled, cautious occasional cleaning with lukewarm water and a little mild soap is possible.
Any soap residue should then be removed carefully, and the pearls dried with a soft cloth.
For strung pearl necklaces, moisture can accumulate in the stringing material and drill holes. Such jewellery should therefore not be soaked unnecessarily.
Ultrasonic cleaners, steam cleaners and aggressive chemical cleaning agents are unsuitable for pearls.
Abrasive polishing products should also be avoided.
Soft, clean storage surfaces are advisable to prevent direct contact with harder jewellery materials.
Very dry or hot locations and prolonged exposure to intense sunlight should be avoided.¹¹
A pearl treated with care can retain its optical qualities for many decades.
What Materials Science Can Learn from Pearls
The internal structure of nacre is of interest beyond gemmology.
Modern materials science also studies it extensively.
Of particular interest is the ability of living organisms to use relatively simple starting materials to create complex composites with impressive properties.
The combination of hard mineral platelets and thin organic interlayers has inspired attempts to develop engineered composite materials.
Research that draws on structural principles found in nature is often described as biomimetics.
Scientists seek to understand how natural materials work and apply those principles in technology.
One aim, for example, is to develop materials that combine high mechanical toughness with low weight.
Remarkably, nacre's unusual properties do not depend on rare chemical elements.
They arise from the exceptionally precise spatial organisation of comparatively ordinary substances.
Nacre therefore provides a striking example of what biologically controlled material formation can achieve.²
What Makes the Material Special
A pearl's properties cannot be explained by its chemical formula alone.
Calcium carbonate forms the mineral basis. The organic matrix controls and stabilises the complex structure. The organisation of the crystals influences both mechanical toughness and optical characteristics.
Biological pigments, trace elements and the particular conditions in which a pearl grew add further variation.
The result is a natural material whose properties emerge from the interaction of chemistry, crystallography, cell biology and physics.
Every pearl is therefore not only the product of a living organism, but the outcome of a complex, biologically controlled process of material formation.
Scientific References
1. Shih, S. C. (2021). Vaterite Found on a Strand of Freshwater Cultured Pearls. Gems & Gemology, vol. 57, No. 4.
https://www.gia.edu/gems-gemology/winter-2021-lab-notes-vaterite-freshwater-cultured-pearls
2. Sun, J. & Bhushan, B. (2012). Hierarchical structure and mechanical properties of nacre: a review. RSC Advances, 2, pp. 7617–7632.
https://doi.org/10.1039/C2RA20218B
3. Otter, L. M. et al. (2023). Growth dynamics and amorphous-to-crystalline phase transformation in natural nacre. Nature Communications, 14, article 2254.
https://doi.org/10.1038/s41467-023-37814-0
4. Gemological Institute of America (GIA). Pearl – Gem Overview. Gemmological properties of pearls, including Mohs hardness.
5. Ozaki, R., Kikumoto, K., Takagaki, M., Kadowaki, K. & Odawara, K. (2021). Structural colors of pearls. Scientific Reports, 11, Artikel 15224.
https://doi.org/10.1038/s41598-021-94737-w
6. Latchere, O. et al. (2018). Influence of water temperature and food on the last stages of cultured pearl mineralization from the black-lip pearl oyster Pinctada margaritifera. PLOS ONE, 13(3), e0193863.
https://doi.org/10.1371/journal.pone.0193863
7. Gemological Institute of America (GIA). Pearl Quality Factors. Explanation of bodycolour, overtones, orient and lustre.
https://www.gia.edu/pearl-quality-factor
8. Wang, Z., Adzigbli, L., Zheng, Z., Yang, C. & Deng, Y. (2020). How cultured pearls acquire their colour. Aquaculture Research, 51(10), pp. 3925–3934.
https://doi.org/10.1111/are.14765
9. Gemological Institute of America (GIA) (2024). Chemical Analysis in the Gemological Laboratory: XRF and LA-ICP-MS. Gems & Gemology, Winter 2024.
https://www.gia.edu/gems-gemology/winter-2024-chemical-analysis
10. Takaishi, K., Tazawa, S. & Yazaki, J. (2026). A study on pearl deterioration and its causes. Abstracts of Lectures at the 2026 Annual Meeting of the Gemmological Society of Japan, pp. 21.
https://doi.org/10.14915/gsj.48.0_21
11. Gemological Institute of America (GIA). Pearl Care and Cleaning Guide. Expert recommendations on chemical resistance, ageing and cleaning of pearls.
https://www.gia.edu/pearl-care-cleaning
Further scientific literature:
Gim, J. et al. (2021). The mesoscale order of nacreous pearls. Proceedings of the National Academy of Sciences (PNAS), 118(42), e2107477118.
https://doi.org/10.1073/pnas.2107477118
This study shows how an ordered layered structure develops during pearl growth and how local irregularities can be partly compensated for.
Gemological Institute of America (GIA) (2024). Raman Spectroscopy and X-Ray Diffraction: Phase Identification of Gem Minerals and Other Species. Gems & Gemology, Winter 2024.
https://www.gia.edu/gems-gemology/winter-2024-raman-spectroscopy-and-xrd
Technical description of identifying aragonite, calcite and vaterite in pearls using spectroscopic and crystallographic methods.
Natural Pearls and the History of Pearl Cultivation
Pearls are among the oldest materials used for personal adornment. Long before people learnt to cut gemstones or work metals into intricate objects, naturally occurring pearls were valued as ornaments and possessions.
Their exceptional status rested not only on their lustre and beauty, but above all on their rarity.
For thousands of years, pearls could be obtained only by collecting wild molluscs. Whether any particular animal contained a pearl was largely a matter of chance.
Only the scientific investigation of pearl formation eventually made it possible to initiate this natural process deliberately.
Modern pearl cultivation, however, was not the result of a single invention. Its development took place over centuries and drew on observations, experiments and technical advances made by several researchers and cultivators.
Natural Pearls – Rare Discoveries
Natural pearls form in pearl-producing molluscs without deliberate human intervention.
Their development depends on particular biological events, and only a small proportion of wild animals actually produce pearls.
Historically, large numbers of molluscs therefore had to be collected and opened in the hope of finding individual pearls.
The most important traditional pearl-fishing regions included the Persian Gulf, the Red Sea, the Gulf of Mannar between India and Sri Lanka, and various rivers in Europe and Asia. Pearl grounds in Central and South America subsequently became important as well.¹
Natural pearl fishing was a major economic activity in the Persian Gulf in particular.
Pearl divers performed exceptionally demanding physical work. They repeatedly descended without modern breathing apparatus to collect oysters from the seabed.
Their work involved serious risks to their health and safety.
The chance of finding a particularly large, well-shaped and visually fine pearl was small.
Such rarity helped establish the extraordinary economic and social value placed on natural pearls for centuries.
Early Attempts to Produce Pearls Deliberately
Long before the development of modern pearl farming, people had observed that molluscs could cover foreign objects with shell material.
The earliest well-documented techniques for deliberately producing nacre-coated objects originate in China.
During the Song dynasty (960–1279), it was known that small objects placed against the inside of living freshwater mussel shells could be covered with nacre.
Small representations of the Buddha produced in this way became particularly well known.
The shaped objects were positioned between the mantle and the shell's inner surface.
Over time, activity in the mantle tissue coated them with nacre.
After harvesting, these nacre-covered religious figures could be used, for example, as devotional objects.
The so-called Buddha pearls were not completely round pearls grown freely within soft tissue.
Rather, they represent an early form of deliberately produced shell-attached nacreous formations.
Nevertheless, the method marked a significant development.
The ability of a living mollusc to deposit nacre was being used intentionally to create a particular object.²
Carl Linnaeus's Scientific Experiments
During the eighteenth century, European naturalists also began to investigate ways of inducing pearl formation.
The Swedish naturalist Carl Linnaeus (1707–1778) played an important role in this work.
Among other questions, he wanted to know whether intervention in a living mussel could influence the formation of pearls.
He conducted experiments on freshwater mussels.
Small foreign objects were introduced through openings in the shell and secured in such a way that the living tissue could cover them with mineral material.
In 1761, Linnaeus presented his findings to a Swedish commission.
Historical reports indicate that he succeeded in producing small pearls by this method.
The process was laborious, however, and did not yield sufficiently reliable or consistently fine results to establish economically important production.
His work was nevertheless scientifically significant.
It demonstrated that deliberate intervention could affect the formation of pearl-like mineral structures.³
Developments during the Nineteenth Century
Knowledge of mollusc anatomy and the biological formation of pearls improved during the nineteenth century.
A particularly important insight was that pearl-producing cells originate in mantle tissue.
Understanding the pearl sac gradually provided a biological basis for techniques capable of creating not only shell-attached formations, but pearls growing freely within soft tissue.
Towards the end of the nineteenth century, the British marine biologist William Saville-Kent (1845–1908) investigated artificial pearl formation in Australia.
His work included methods that involved inserting foreign objects into molluscs so that nacre would grow over them.
He succeeded in producing shell-attached half-pearls.
Some historical accounts also credit him with early success in producing free cultured pearls.
Whether, and to what extent, his findings directly influenced the methods subsequently adopted in Japan cannot be established conclusively.
Historians assess this question differently.⁴
What is certain is that researchers and cultivators in Europe, Australia and Japan were all investigating the deliberate formation of pearls towards the end of the nineteenth century.
The decisive breakthrough to sustained commercial production ultimately took place in Japan.
The Beginnings of Modern Pearl Cultivation in Japan
Three Japanese pioneers are closely associated with the development of modern pearl farming:
Tatsuhei Mise (1880–1924), Tokichi Nishikawa (1874–1909) and Kokichi Mikimoto (1858–1954).
At the beginning of the twentieth century, Mise and Nishikawa developed methods for producing approximately spherical pearls growing freely in mollusc tissue.
The crucial innovation was to create the biological conditions required for a pearl sac, rather than merely insert a foreign object.
A suitable nucleus was combined with a small piece of mantle tissue.
The transplanted epithelial cells could form a pearl sac, whose cells gradually deposited nacre around the nucleus.
This principle remains fundamental to many forms of pearl cultivation today.
Mise received a Japanese patent for such a method in 1907. Nishikawa developed a closely related process independently.
The two approaches later became known collectively as the Mise–Nishikawa method.⁵
Kokichi Mikimoto had already been experimenting with pearl production for some years.
In 1893, with scientific guidance from biologist Kakichi Mitsukuri, he succeeded in producing shell-attached half-pearls.
He received a Japanese patent for a corresponding method in 1896.
Over the following decades, Mikimoto continued developing his farms and the commercial production of cultured pearls.
From 1916 onwards, he also used the technique associated with Mise and Nishikawa to produce free cultured pearls.
This laid the groundwork for increasingly reliable production of round cultured pearls.
By the early 1920s, such pearls were reaching international jewellery markets in significant quantities.⁵ ⁶
Mikimoto is consequently regarded as a central figure in the history of the modern pearl industry.
The underlying cultivation technique, however, was the result of several scientific and technical developments involving different individuals.
The Transformation of International Pearl Trading
The arrival of modern cultured pearls fundamentally changed the international pearl trade.
Previously, supplies had depended almost entirely on rare finds from wild molluscs.
Deliberate cultivation made it possible to plan production more reliably and to supply larger numbers of pearls.
Cultured pearls could be sold at substantially lower prices than comparable natural pearls.
They thus became accessible to a growing number of people who previously could not have afforded fine pearl jewellery.
The transition was not without resistance.
Traders dealing in traditional natural pearls initially viewed the increasing availability of cultured pearls with concern.
A further difficulty was that many cultured pearls were externally almost indistinguishable from natural pearls.
There was therefore a strong commercial demand for reliable gemmological methods of identification.
Research into pearls' internal structures and the development of appropriate testing techniques became increasingly important.
With the wider use of X-ray imaging, natural and cultured pearls could be investigated by their differing internal growth features.
The rise of pearl cultivation thus affected not only the jewellery trade, but also stimulated scientific pearl research.⁷
The Decline of Traditional Natural Pearl Fishing
As cultured pearls became established, traditional natural pearl fishing gradually lost economic importance.
Cultivation alone, however, did not cause this change.
Various wild pearl-oyster populations had already declined substantially through intensive harvesting.
Economic developments, the Great Depression beginning in 1929 and the Second World War also profoundly disrupted international trading in luxury goods.
During the twentieth century, cultured pearls largely replaced natural pearls in the ordinary jewellery market.
Natural pearls did not disappear from the market entirely.
Exceptionally fine and historically significant specimens remain sought-after collectors' items and can still command extraordinary prices.⁸
The Worldwide Spread of Pearl Cultivation
Following the commercial success of Japanese pearl farming, cultivation methods spread progressively to other parts of the world.
Techniques were adapted to different mollusc species, climatic conditions and economic circumstances.
Alongside Japanese marine pearl cultivation, major farming regions developed in Australia, South-East Asia and the Pacific.
Modern freshwater pearl cultivation evolved in parallel.
China, in particular, assumed a leading role during the second half of the twentieth century.
Improvements in techniques, rearing conditions and the selection of suitable mussel species allowed substantial increases in both production volumes and quality.
Where earlier cultivation had concentrated on producing increasingly uniform pearls, later developments also provided greater scope to influence size, shape and colour.
An increasingly varied range of cultured pearls emerged.
The history of these developments is best explored in relation to individual pearl types. Their specific cultivation methods are therefore discussed in the corresponding specialist chapters.⁹
Natural and Cultured Pearls – Two Routes to Biological Pearl Formation
Despite their different histories, natural and cultured pearls are based on the same fundamental biological processes.
In both cases, living cells produce the mineral and organic constituents from which the pearl develops.
The essential distinction lies in how that process begins.
A natural pearl starts forming without deliberate human intervention.
In a cultured pearl, the biological process is initiated by the deliberate introduction of suitable tissue and, where appropriate, a nucleus.
A cultured pearl is therefore not an artificial replica of a natural pearl.
It is produced by a living organism and has a biologically grown mineral and organic structure.
Pearl imitations, by contrast, are manufactured from other materials to resemble pearls in appearance.
Pearl cultivation did not invent an artificial replacement.
Rather, it made use of a naturally occurring biological process that people had come to understand scientifically.
The Significance of Pearl Cultivation Today
Modern pearl cultivation combines biological research, specialised craftsmanship and the long-term care of living organisms.
Despite technical advances, the growth of an individual pearl cannot be controlled completely.
The characteristics of the molluscs used, the skill of the cultivators and the environmental conditions during growth all influence the outcome.
Not every operated mollusc produces a usable pearl. Nor can the exact size, shape, colour or surface characteristics of a single pearl be predicted with certainty.
The history of pearl farming is therefore more than a succession of technical inventions.
It shows how people have learnt to understand a complex biological process and use its potential deliberately.
Despite the human intervention involved, a modern cultured pearl remains a naturally grown product of a living organism.
Scientific and Historical References
1. Gemological Institute of America (GIA). Pearl History and Lore.
Overview of the historical importance of natural pearls and their principal harvesting regions.
https://www.gia.edu/pearl-history-lore
2. Zhu, C., Southgate, P. C. & Li, T. (2018). Production of Pearls. In: Goods and Services of Marine Bivalves. Springer, pp. 73–93.
https://doi.org/10.1007/978-3-319-96776-9_5
3. Linnæus and the Production of Artificial Pearls. (1930). Nature, 126, pp. 456.
Historical account of Linnaeus’s experiments and their presentation in 1761.
https://doi.org/10.1038/126456a0
4. Western Australian Museum. Growing Pearls.
Museum documentation of early pearl cultivation, William Saville-Kent and the development of Japanese methods.
https://museum.wa.gov.au/explore/lustre-online-text-panels/growing-pearls/index.html
5. Gemological Institute of America (GIA) (2014). History of Cultured Pearls – Part 1.
Historical account of the development of the Mise–Nishikawa method and the work of Kokichi Mikimoto.
https://4cs.gia.edu/en-us/blog/history-cultured-pearls-part-1/
6. Nagai, K. (2013). A history of the cultured pearl industry. Zoological Science, 30(10), pp. 783–793.
https://doi.org/10.2108/zsj.30.783
7. Gemological Institute of America (GIA) (2024). Applications of X-Ray Radiography and X-Ray Computed Microtomography in Gemology. Gems & Gemology, Winter 2024.
https://www.gia.edu/gems-gemology/winter-2024-x-ray-imaging
8. Sato, A. & Cartier, L. E. (2023). The value of cultured pearls: evolution and current trends. Swiss Gemmological Institute SSEF, Facette 28.
https://www.ssef.ch/jp/the-value-of-cultured-pearls-evolution-and-current-trends/
9. Zhu, C., Southgate, P. C. & Li, T. (2018). Production of Pearls. See reference 2.
Additional Historical Reading
Ericson, K. (2020). The Life and Times of Patent No. 2,670: Industrial Property and Public Knowledge in Early Twentieth-Century Japan. In: Patent Cultures. Cambridge University Press, pp. 319–340.
This study in the history of science examines Mikimoto’s 1896 patent and contemporary legal disputes about patents for pearl-cultivation techniques.
https://doi.org/10.1017/9781108654333.016
Different Types of Pearls
Pearls occur in an extraordinary range of shapes, colours, sizes and optical appearances.
They form in different species of mollusc, whose biological characteristics affect both their structure and appearance.
Over the centuries, numerous terms have emerged. Some refer to the pearl-producing animal's habitat, others to a particular species, a geographical origin or a method of cultivation.
There are also trade names used primarily to distinguish particular products.
A scientifically meaningful classification must therefore distinguish between these different criteria.
The Fundamental Categories
Pearls can be classified according to several independent characteristics.
According to how they form:
- Natural pearls develop without deliberate human intervention.
- Cultured pearls develop through a biological process deliberately initiated by people.
According to the mollusc's habitat:
- Freshwater pearls are formed by molluscs living in freshwater environments.
- Saltwater or marine pearls are formed by marine molluscs.
According to mineral structure:
- Nacreous pearls have the characteristic layered structure of mother-of-pearl.
- Non-nacreous pearls have other mineral arrangements, such as fibrous or cellular structures.
These categories are not mutually exclusive.
A pearl may, for example, be both a natural marine pearl and non-nacreous.
Natural versus cultured describes the circumstances of formation. Freshwater versus marine describes the animal's environment.
Several attributes may therefore need to be considered together to describe a pearl accurately.¹
Freshwater Pearls
Freshwater pearls develop in suitable species of freshwater mussels.
Members of the family Unionidae are particularly important in modern commercial pearl cultivation.
Freshwater cultured pearls are distinguished by their varied shapes and natural colours.
Alongside white and cream, these include pink, peach, violet and brownish hues.
Their sizes and surface textures may also differ substantially.
Traditional techniques mainly produced non-bead-cultured pearls. Today, however, larger freshwater cultured pearls with inserted nuclei are increasingly common.
Technical advances have allowed some of these pearls to attain sizes, shapes and lustre formerly associated principally with marine cultured pearls.²
Biwa Pearls
The name ‘Biwa pearl’ originally refers to freshwater pearls cultivated in Lake Biwa, Japan.
They became known for their varied natural colours and characteristic shapes.
The trade sometimes applies the name to similar-looking freshwater cultured pearls from elsewhere.
Such usage is, however, geographically imprecise.
The original designation refers to Lake Biwa itself, not to any particular freshwater pearl shape.³
Kasumiga Pearls
Kasumiga pearls originally come from cultivation in Japan's Lake Kasumigaura.
They are valued for distinctive natural colours, unusual surface structures and, in some instances, a metallic-looking lustre.
Cultivation uses, among other things, hybrids involving suitable Japanese and Chinese freshwater mussels.
‘Kasumigaura’ describes geographical origin. Similar pearls grown elsewhere should not be described as Japanese Kasumigaura pearls without evidence of that provenance.³
Ming and Edison Pearls
Ming and Edison pearls belong to the modern group of bead-cultured freshwater pearls.
They frequently attain larger diameters and may display intense natural colours, pronounced overtones and strong lustre.
The names are sometimes used together or in similar commercial contexts.
They do not designate two distinct zoological pearl species.
‘Edison pearl’ originally refers to a group of bead-cultured freshwater pearls developed and produced by the Chinese company Zhejiang Grace Pearl Jewellery.
‘Ming pearl’, by contrast, is used more broadly for larger, high-quality bead-cultured freshwater pearls from other producers.
A GIA gemmological study published in 2021 explicitly described this distinction.⁴
The cultivation methods, biological origins and differences between these products are dealt with more fully in the relevant specialist chapters.
Marine Pearls
Marine pearls develop in saltwater molluscs.
Commercial cultivation of traditional nacreous pearls is concentrated on a relatively small number of species in the genera Pinctada and Pteria.
The best-known groups include Akoya, Tahitian and South Sea pearls.
They differ in the molluscs producing them, their typical sizes, colours and optical characteristics.
Other regionally significant and sometimes rare pearl types also occur.²
Akoya Pearls
Akoya pearls are cultivated primarily in Pinctada fucata.
They are especially known for their often near-spherical shape and pronounced, mirror-like lustre.
Their natural colour palette consists chiefly of pale shades.
Modern Akoya cultivation is historically closely connected with Japan, but other production areas include China and Vietnam.
Akoya pearls are traditional examples of bead-cultured marine pearls.
Tahitian Pearls
Tahitian pearls are cultivated in the black-lipped pearl oyster, Pinctada margaritifera, particularly in French Polynesia.
Their extensive natural colour range is characteristic.
Alongside dark grey and black they may exhibit green, violet, blue and brown hues.
Pronounced overtones often give them an especially varied appearance.
‘Tahitian pearl’ is an established geographical and trade designation, not the name of a separate zoological species.
South Sea Pearls
South Sea pearls grow in the large pearl oyster Pinctada maxima.
The species is cultivated particularly in Australia and parts of South-East Asia.
Its size allows comparatively large cultured pearls to develop.
White, silvery and golden South Sea pearls are especially familiar.
Their colours are connected partly with the biological characteristics of the silver-lipped and gold-lipped forms of Pinctada maxima.
Cortez Pearls
Cortez pearls are a distinctive group of marine cultured pearls from Mexico's Gulf of California.
They are cultivated in the rainbow-lipped pearl oyster, Pteria sterna.
They are known for sometimes unusually intense natural colours and metallic-looking lustre.
The designation thus combines a geographical origin with a particular cultured-pearl product.
Special Pearl Forms and Cultured Products
Not every pearl trade term describes a zoological origin.
Some terms instead refer to the way a pearl is formed or to subsequent processing.
Keshi Pearls
The Japanese word ‘keshi’ is used particularly for small, often irregular pearls without an inserted spherical bead nucleus.
In modern marine pearl farming, such pearls may arise as by-products.
For example, a mollusc may expel the originally implanted bead while an already formed pearl sac continues to deposit nacre.
Keshi cultured pearls thus develop without the intended solid nucleus, although they may contain organic residues or other small inclusions.
Keshi is not a distinct mollusc species.
Nor should the name automatically be interpreted as meaning a natural pearl.
CIBJO therefore recommends explicitly distinguishing natural keshi pearls from keshi cultured pearls.¹
Mabé Pearls
Mabé pearls are shell-attached cultured products.
Their production first creates a raised nacreous formation on the inner surface of a mollusc shell.
After harvesting, the grown part is separated from the shell and generally processed further.
The cavity is filled and a backing attached.
The finished jewellery component consequently has a composite construction.
Mabé pearls differ both from free-grown pearls and from ordinary pearl imitations: their visible nacreous surface was grown biologically by a living mollusc.
CIBJO accordingly classifies mabé pearls among composite, shell-attached cultured products.¹
Other Naturally Occurring Pearls
Not all pearls originate in the molluscs used for conventional pearl cultivation.
Various marine gastropods and other bivalves can also produce pearls.
Abalone Pearls
Abalone pearls form in marine gastropods of the genus Haliotis.
These animals' shells are known for exceptionally colourful, iridescent nacre.
Their pearls may likewise display intense combinations of green, blue, violet and gold.
Natural abalone pearls frequently have irregular, elongated or horn-like shapes.
Deliberate abalone pearl cultivation also exists, particularly for shell-attached forms.
The production of free bead-cultured abalone pearls has also been documented scientifically.⁵
Conch Pearls
Conch pearls originate particularly in the large marine gastropod Aliger gigas, called Strombus gigas or Lobatus gigas in older publications.
They do not have the traditional nacreous construction of successive aragonite platelets.
Instead, they exhibit a different, mainly fibrous mineral structure.
Their colours range from white and cream to shades of pink and orange.
Some have a particularly characteristic flame-like visual appearance known as flame structure.
Melo Pearls
Melo pearls form in large marine gastropods of the genus Melo.
They too are non-nacreous pearls.
Yellow, orange and brownish colours are common.
As in conch pearls, their internal mineral arrangement can produce a flame-like optical effect.
Conch and melo pearls demonstrate that a pearl need not possess the characteristic iridescence of nacre to be recognised gemmologically as a pearl.⁶
Natural Pearls, Cultured Pearls and Imitations
The jewellery trade also offers products made to resemble natural or cultured pearls.
These must be distinguished from biologically grown pearls.
A pearl imitation does not result from the natural pearl-forming process within a living mollusc.
Its appearance is instead reproduced using appropriate starting materials and manufacturing processes.
Glass, plastics or worked shell material may be used as a base.
Surfaces may be coated to imitate the sheen, colour and reflection of a naturally formed pearl.
The distinction between cultured pearls and pearl imitations does not depend solely on the chemical composition of the starting material.
The essential question is whether the pearl itself developed through a living organism's biological growth process.¹
Shell-Core Pearls and Other Pearl Imitations
One group of imitations is made using mollusc shell material.
For a so-called shell-core pearl, a core may be shaped from shell material and then coated with an artificially applied surface layer.
Different constituents and coatings may be used according to the manufacturing method.
Although these products contain material of biological origin, they are not biologically grown cultured pearls.
A GIA examination published in 2014 showed that such shell-core pearls can closely resemble South Sea and Tahitian cultured pearls externally.
Microscopy nevertheless revealed the artificial coating, while gemmological tests also identified differences in internal structure.⁷
Various trade names are used for these products, including ‘shell pearls’.
Transparent material descriptions are particularly important.
For example, the name ‘South Sea shell pearl’ does not mean that the item is a biologically grown South Sea cultured pearl from Pinctada maxima.
It identifies a group of pearl imitations whose materials, manufacture and appearance must be distinguished from a genuine South Sea cultured pearl.
This distinction is not intended as a blanket judgement against the quality of imitations.
Man-made materials can also possess appealing design and practical characteristics.
What matters is that buyers can understand what the product actually consists of.
Natural Colours and Subsequent Treatments
Another distinction concerns pearl colour and treatment.
Natural and cultured pearls may be processed or treated after formation to alter certain optical properties.
Known methods include bleaching, dyeing and irradiation.
Treating a biologically grown pearl does not automatically turn it into a pearl imitation.
It remains a natural or cultured pearl whose appearance has been altered subsequently.
Distinguishing natural from treated colours is nevertheless important for gemmological examination and transparent product descriptions.
Particularly with unusually intense colours, scientific methods can be used to investigate indications of treatment.
These include optical spectroscopy, Raman spectroscopy and the study of characteristic fluorescence responses.⁴
Why Accurate Terminology Matters
The diversity of pearls makes precise terminology especially important.
Names may refer to:
- The species in which a pearl grew.
- Its habitat or geographical origin.
- Whether growth began naturally or was deliberately initiated.
- The nucleus and cultivation technique used.
- Its mineral structure.
- A particular commercial name.
These criteria should not be confused.
With names such as Biwa, Kasumiga, Ming, Edison, Keshi and Mabé, it is especially important to understand what each actually means.
International gemmological organisations and trade bodies have accordingly developed guidance and classification systems for transparent descriptions.
An important reference is CIBJO's Pearl Book, which defines terminology for natural pearls, cultured pearls, composite cultured products and pearl imitations.¹
Understanding these differences is useful not only for scientific classification.
It also helps people recognise the distinctive characteristics of individual pearls and compare different materials on an informed basis.
Scientific References
1. CIBJO – The World Jewellery Confederation (2024). The Pearl Book – Natural, Cultured, Composite and Imitations of Pearls: Terminology and Classification. November 2024 edition.
https://cibjo.org/wp-content/uploads/2024/11/2024-Pearl-Book-Nov-3.pdf
2. Gemological Institute of America (GIA). Different Pearl Types Explained: Akoya, South Sea, Tahitian & Freshwater Pearls.
https://www.gia.edu/gia-news-research/differences-between-pearl-types
3. Abduriyim, A. (2018). Cultured Pearls from Lake Kasumigaura: Production and Gemological Characteristics. Gems & Gemology, 54(2).
4. Zhou, C. et al. (2021). Detection of Color Treatment and Optical Brightening in Chinese Freshwater “Edison” Pearls. Gems & Gemology, 57(2), pp. 124–134.
5. Wentzell, C. Y. (1998). Cultured Abalone Blister Pearls from New Zealand. Gems & Gemology, 34(1).
https://www.gia.edu/gems-gemology/fall-1998-abalone-blister-pearls-new-zealand-wentzell
Additionally: Bead Cultured Abalone Pearls from Chile. GIA, Gems & Gemology (2023).
https://www.gia.edu/gems-gemology/spring-2023-gemnews-bead-cultured-abalone-pearls-chile
6. Gemological Institute of America (GIA) (2024). Analysis of Gemstones at GIA Laboratories. Gems & Gemology, Winter 2024.
https://www.gia.edu/gems-gemology/winter-2024-gemstone-analysis
7. Zhou, J. Y. & Zhou, C. (2014). Shell Pearl as a Pearl Imitation. Gems & Gemology, 50(2), Lab Notes.
https://www.gia.edu/gems-gemology/summer-2014-labnotes-shell-pearl
Gemmology and the Assessment of Pearls
Pearls are among the few jewellery materials formed entirely through biological processes within a living organism.
Their unusual properties make them interesting not only to the jewellery trade, but also to researchers investigating their formation, composition, origins and quality.
An important discipline in this work is gemmology, the scientific study of gemstones and other materials used in jewellery.
Gemmology makes it possible to examine pearls systematically, describe their properties and distinguish different types.
Scientific identification, gemmological quality assessment, economic value and design value must nevertheless be distinguished.
These considerations are related, but are not interchangeable.
What Is Gemmology?
Gemmology is an interdisciplinary science concerned with the examination, identification and characterisation of gemstones and other jewellery materials.
It developed historically from mineralogy in particular, but today extends well beyond the study of mineral gemstones.
It draws on mineralogy, crystallography, chemistry, physics, geology and biology.
Diamonds, rubies and emeralds, for instance, are mineral materials, whereas pearls, coral and amber are of biological origin.
In gemmology, such substances are often described as organic gem materials or organic jewellery materials.
Pearls present a particularly interesting case.
Although they consist largely of crystalline calcium carbonate, a pearl as a whole is not a single mineral crystal. It is a biologically produced composite.
Its examination therefore requires knowledge of its mineral components as well as an understanding of its biological formation.¹
Modern gemmology includes identifying materials, examining their properties and recognising treatments or imitations.
The discipline also develops and refines scientific testing techniques.
What Gemmologists Investigate in Pearls
A gemmological examination begins with several fundamental questions.
Is the specimen a pearl grown by a living mollusc, or a manufactured imitation?
Did it form without human intervention, or is it a cultured pearl?
Did it originate in a freshwater or marine mollusc?
Does it have a conventional nacreous structure or a different mineral construction?
Has its natural colour been altered after formation?
These questions concern the identity and nature of the material.
Quality assessment is a separate matter.
It considers characteristics such as size, shape, colour, lustre, surface quality and, where relevant, nacre thickness and quality.
Only on the basis of such findings can a further economic appraisal be undertaken.
Scientific testing is therefore not the same thing as establishing a selling price.
How Do Gemmologists Examine a Pearl?
Modern gemmology uses a wide range of investigative methods.
Some assess externally visible features; others reveal hidden internal structures or provide information about chemical composition.
Visual Examination and Microscopy
An examination usually begins with viewing the pearl under suitable, preferably reproducible lighting conditions.
Its shape, colour, lustre and visible surface features are considered.
A microscope makes it possible to investigate small growth structures, indentations, scratches and other features more closely.
Drill holes can also yield important information.
Under suitable magnification, for example, they may reveal signs of artificial coatings, surface treatments or damage.
Microscopy alone, however, is not always sufficient to distinguish a natural pearl reliably from a cultured pearl.
That often requires examination of its internal structure.
X-Ray Examination
X-ray radiography is one of the most important methods for distinguishing natural and cultured pearls.
X-rays penetrate the specimen and are absorbed to varying degrees according to its density, composition and structure.
Internal features invisible from outside can therefore be revealed.
Natural pearls may exhibit concentric growth structures or irregularly arranged mineral and organic zones.
In a conventional bead-cultured pearl, the implanted nucleus and the surrounding biologically grown nacre are often visible.
Non-bead-cultured pearls, by contrast, may have quite different internal features.
In difficult cases, X-ray micro-computed tomography (micro-CT) can be used.
This technique reconstructs a three-dimensional representation of the pearl's interior.
It can reveal spatial relationships that are not clear in an ordinary two-dimensional radiograph.²
Interpreting these features requires expertise, since the internal structures of natural pearls and some cultured pearls can overlap.
Spectroscopic Methods
Other important techniques depend on interactions between electromagnetic radiation and the pearl's constituents.
Raman spectroscopy examines changes in the frequency of light scattered by a material.
The resulting characteristic spectra can distinguish between different forms of calcium carbonate, including aragonite, calcite and vaterite.
UV–visible spectroscopy examines the absorption or reflection of ultraviolet and visible light.
It may provide evidence of natural pigments or certain subsequent colour treatments.
Fluorescence can also be investigated.
Some natural substances and artificial treatments alter the way pearls fluoresce.
A single spectrum or unusual fluorescence response is not always enough for a definite identification. Results from different tests have to be interpreted together.³
Chemical Analysis
In X-ray fluorescence analysis (XRF), characteristic X-rays emitted by chemical elements within the sample are measured.
This can reveal certain trace elements.
The relative presence of strontium and manganese, for example, may indicate whether a pearl originated in freshwater or a marine environment.
Specialised laboratories also employ other chemical analytical techniques.
Results must be interpreted in relation to the pearl type under examination.
A particular chemical composition cannot automatically establish the exact geographical origin.
DNA Analysis and Age Determination
Biological testing methods have also advanced in recent years.
One promising approach involves analysing very small quantities of DNA that may remain preserved within a biologically grown pearl.
With suitable procedures and reference data, it may in certain cases be possible to identify the mollusc species from which the pearl originated.
The Swiss Gemmological Institute SSEF has helped develop such methods in collaboration with scientific partners.
Another possibility is age determination by radiocarbon dating.
This involves examining the relationship between radioactive and stable carbon isotopes to obtain information about the age of biological material.
These techniques are particularly useful when studying historical pearls and significant museum or private collections.
They are not part of ordinary visual pearl quality grading, and some analyses may require the removal of small material samples.⁴
Leading Gemmological Institutions
Specialised gemmological institutions undertake scientific examinations of pearls.
Among internationally recognised organisations are the following.
Gemological Institute of America (GIA)
Founded in 1931, this American institute undertakes research, education and gemstone examination.
In the field of pearls, it has contributed in particular to systematic quality descriptions and the development of modern analytical methods.
Gemmological Association of Great Britain (Gem-A)
Gem-A is one of the long-established professional bodies for gemmological education and publications.
It teaches the scientific principles and methods used to examine mineral and organic jewellery materials.
Swiss Gemmological Institute SSEF
The Swiss Gemmological Institute SSEF is an independent, non-profit foundation based in Basel.
The abbreviation SSEF derives from its German foundation name, Schweizerische Stiftung für Edelstein-Forschung.
The institute specialises in scientific testing of gemstones and pearls.
Its pearl examinations include distinguishing natural from cultured pearls, investigating freshwater or saltwater origin and identifying detectable treatments.
Specialised tests may provide additional information, for example about mollusc species or the age of a pearl.
SSEF reports document scientific findings, not commercial price valuations.⁵
Another important organisation is CIBJO (World Jewellery Confederation).
CIBJO is not a gemmological testing laboratory. It is an international jewellery-sector body which, among other activities, develops terminology and standards for jewellery materials.
Its Pearl Book is an important reference for the correct classification and description of natural pearls, cultured pearls and imitations.
Assessing Gemmological Quality
No single characteristic determines a pearl's quality.
Assessment considers several factors together.
The GIA has developed a system of seven quality and value factors known as the GIA 7 Pearl Value Factors.
They are:
- Size
- Shape
- Colour
- Lustre
- Surface quality
- Nacre quality
- Matching, when several pearls are used together
The system allows pearls to be described and compared in a structured manner.
It is not a mathematical formula that automatically determines an individual pearl's monetary value.⁶
Size
Pearl dimensions are usually given in millimetres.
For round and near-round pearls, diameter is the principal measurement.
For elongated, drop-shaped or otherwise irregular pearls, several dimensions may be needed to describe the size adequately.
Size is an important value factor.
Within the same pearl type, larger specimens are often rarer, and therefore more expensive, when other qualities are comparable.
Producing larger cultured pearls may require suitable molluscs, longer growth periods and favourable conditions.
Comparing sizes directly across different pearl types is therefore of limited value.
An Akoya pearl that is unusually large for its species may be of a size that is commonplace for a South Sea pearl.
Pearl weight may also be stated alongside dimensions.
Units include grams, carats and the traditional Japanese momme.
One carat equals 0.2 grams; one momme equals 3.75 grams.
The historical pearl grain is also used for natural pearls. One pearl grain is one quarter of a carat, or 0.05 grams.
It must not be confused with the ordinary avoirdupois grain, which is approximately 0.0648 grams.⁷
Shape
Pearls occur in an exceptionally wide variety of shapes.
Common descriptions include round, near-round, oval, drop, pear, button, baroque and semi-baroque.
Some have pronounced ring-like growth features and are called circled pearls.
Shape develops as the pearl grows inside the mollusc.
In bead-cultured pearls, the inserted nucleus often influences the basic outline.
Further nacre deposition can nevertheless result in substantial departures from the original bead shape.
Perfectly round pearls are often particularly sought after and expensive when other qualities are equal.
This reflects both their relative rarity and a longstanding preference for symmetrical forms.
An irregular shape does not, however, necessarily imply inferior material quality.
Baroque pearls can possess nacre, lustre and natural colour as fine as those of round examples.
The gemmological description of shape must therefore be distinguished from its suitability for a particular jewellery composition.
Colour
A pearl's colour consists of several optical components.
Bodycolour refers to the basic colour impression.
A pearl may also display one or more overtones.
Orient denotes an iridescent play of colour visible at or immediately beneath the surface.
These three features were discussed in the chapter on chemical and physical properties.
Gemmological assessment considers aspects such as consistency, intensity and whether the colour is natural or has been treated.
A preference for a particular hue, however, is not determined by science alone.
Fashion, cultural traditions and personal taste also play a part.
Bodycolour on its own is therefore not sufficient evidence of superior material quality.
Viewing should take place under appropriate and as far as possible consistent lighting.
Background colour, the colour temperature of the light and nearby surfaces can all influence the perceived hue.
Reliable comparisons therefore depend more on reproducible viewing conditions than on using one fixed background for every type of pearl.⁶
Lustre
Lustre is among the most important optical quality factors.
It describes the brightness and sharpness of reflections on and close to the pearl's surface.
A pearl with strong lustre shows bright, clearly defined reflections.
With weak lustre, reflections look more diffuse, flatter and less contrasting.
The GIA uses five grades of lustre:
- Excellent
- Very Good
- Good
- Fair
- Poor
These categories describe the quality of the visible reflections.
Different pearl types can nevertheless display characteristically different appearances.
Akoya pearls often have sharp, mirror-like reflections.
Fine South Sea pearls may instead display a softer, silkier lustre.
Lustre must therefore be interpreted in relation to the pearl type.
Nacre thickness by itself is not sufficient to establish quality.
The structure, organisation and condition of the outermost nacre layers are also important.⁶
Surface Characteristics
The surface of a biologically grown pearl is rarely perfectly uniform.
During growth, small projections, depressions, folds, concentric growth zones or irregular mineral deposits can arise.
Gemmology describes these as surface features or growth features.
Conventional quality assessment considers how many such features are present, how conspicuous they are and how far they affect the pearl's appearance or durability.
Different kinds of surface feature must nevertheless be distinguished.
A small natural projection is not equivalent to a deep crack.
A fold formed during nacre deposition is likewise different from damage caused later by abrasion or mechanical stress.
Some features are primarily visual.
Others may weaken the material or indicate inadequate nacre formation.
Deep cracks, flaking nacre or severely damaged areas in which the bead nucleus is exposed are particularly concerning.
Such defects are not simply matters of individual taste.
They can genuinely affect the pearl's durability.
A sound gemmological assessment must therefore distinguish natural growth features, optical irregularities and damage relevant to material integrity.⁸
Nacre Quality and Thickness
The quality of the grown nacre is especially important in bead-cultured pearls.
The implanted nucleus becomes coated as the pearl sac deposits nacre.
Thickness varies according to species, cultivation technique and growth period.
A nacre layer that is too thin or insufficiently developed may impair both appearance and durability.
Under some circumstances the underlying bead may be visible through the nacre.
Irregular deposits and poorly formed layers can also detract from appearance.
A thick layer, however, does not automatically guarantee excellent lustre.
The quality of its mineral and organic structure is also essential.
Assessment of non-bead freshwater cultured pearls is different.
Because no large spherical shell bead is inserted, their quality cannot be assessed by the same simple relationship between bead diameter and outer nacre layer.
Gemmological assessment must therefore take account of the particular type of pearl.
Recent GIA publications also show that some grown surface features that initially resemble marks left by processing may actually result from unusual forms of natural nacre growth.⁹
Matching Pearls in a Jewellery Piece
Jewellery incorporating several pearls raises another quality factor: matching.
In traditional pearl necklaces, a high degree of similarity in size, shape, colour, lustre and surface quality is often sought.
A closely matched strand may command a high price because many individual pearls with comparable characteristics must be selected.
Matching need not, however, mean absolute uniformity.
Deliberately chosen differences can create a harmonious overall appearance.
For example, pearls of different sizes or colours can be arranged according to a coherent compositional principle.
In such jewellery, the important factor is not the identity of every individual pearl, but their thoughtful selection and how their characteristics work together.
The GIA also recognises that intentionally varied jewellery arrangements require different design criteria from completely uniform pearl strands.⁶
The Quality of Drilling
In addition to the seven GIA value factors, drill holes have particular practical importance in jewellery making.
Their diameter, placement and direction should suit the pearl's intended use.
A misplaced or angled hole can make a pearl sit at an unintended angle or position.
The edges of the holes also require attention.
Chipping, cracking or other damage around a hole can impair both appearance and durability.
Careful jewellery composition therefore requires considering not only the pearl itself, but also whether it can be used appropriately in the planned piece.
Drilling quality is not a separate GIA 7 Pearl Value Factor, but is a significant consideration in practical jewellery manufacture.
Grading – Assigning Quality Categories
Different systems are used internationally to grade pearls.
Letter-based systems such as A, AA and AAA are especially widespread in the trade.
Some suppliers also use additional categories such as AA+ or AAAA.
Such grades may have defined meanings within a particular business or scheme.
There is, however, no single worldwide AAA system in which every supplier applies the same criteria across all types of pearls.
An AAA pearl from one supplier does not necessarily have the same characteristics as an AAA pearl from another.
The GIA does not use a general AAA-style letter ranking for its scientifically oriented pearl quality classification. Instead, it describes the seven value factors separately.
This allows the characteristics of an individual pearl to be assessed in greater detail rather than reduced to a single letter.
CIBJO likewise contributes to international efforts to standardise gemmological terminology and quality descriptions.¹⁰
Buyers should therefore avoid relying exclusively on an AAA label.
A clear account of the pearl's actual characteristics is more informative.
Scientific Quality and Market Value
Gemmological examination provides an important basis for economic appraisal.
It does not, however, determine the selling price automatically.
Rarity, demand, origin and conditions in the international pearl market also influence value.
For natural pearls, reliable confirmation of natural formation can have a particularly substantial effect.
Historical associations and documented provenance can also matter for certain specimens.
For cultured pearls, production costs, the availability of particular sizes and demand for certain colours and shapes influence pricing.
The most expensive pearl is not necessarily the one that an individual finds most appealing.
Conversely, a pearl of unusual shape or with pronounced growth features need not be of limited design interest.
Scientific quality, market price and personal appreciation are different perspectives.
The Approach to Composition at LARUSCA Perlenschmuck®
At LARUSCA, the established scientific quality factors are taken seriously, but they are not weighted exclusively according to their importance in conventional commercial grading.
The condition, lustre, colour and durability of a pearl are important considerations when it is selected for jewellery.
At the same time, we regard pearls' natural diversity as a fundamental part of their potential for composition.
This is particularly evident in surface characteristics.
Conventional grading often favours surfaces that are as uniform and free from visible features as possible. Natural growth markings, however, may be aesthetically interesting within a particular jewellery composition.
An irregularly formed surface can reflect and scatter light differently from a perfectly smooth sphere.
It may produce lively reflections that change as the viewing angle changes.
Unusual shapes can also offer distinctive possibilities for composition.
An elongated, asymmetric or baroque pearl has a spatial character of its own, which can be deliberately incorporated into a piece of jewellery.
Not every departure from geometric uniformity should therefore be regarded as a flaw in a composition.
Actual material damage must be distinguished clearly from such variation. Deep cracks, flaking nacre or other defects that affect durability do not become desirable quality features simply because a piece is considered from a design perspective.
At LARUSCA, the emphasis is on consciously selecting and arranging suitable pearls.
An individual pearl may be chosen for its lustre, colour, shape or an especially interesting growth feature.
Perfect uniformity of every characteristic is not the sole objective; what matters is how the characteristics work together within a coherent composition.
This approach is not at odds with gemmology.
It simply distinguishes the scientific description of a material from its creative use.
Gemmology explains the characteristics a pearl possesses.
Jewellery composition determines how those characteristics are brought into play.
The Limits of Quality Assessment
Scientific analysis makes it possible to describe pearls systematically and transparently.
It can establish, for example, whether a pearl has strong lustre, whether its surface has structural damage, or whether its colour may have been treated.
It can also help explain why some characteristics are considered especially rare or valuable within the pearl trade.
Science cannot, however, determine which shape or combination of colours an individual will find most beautiful.
Nor can the effect of a finished jewellery piece be reduced entirely to the measured quality of its constituent pearls.
This is a fundamental distinction between examining a jewellery material and working creatively with it.
Gemmology gives us knowledge of a pearl's properties. Using those properties in a composition opens up further possibilities for individuality, expression and personal preference.
Scientific References
1. Gemmological Association of Australia. What is Gemmology? Professional definition and scientific foundations of gemmology.
2. Hänni, H. A., Krzemnicki, M. S., Chalus, P., Karampelas, S. & Friess, S. D. (2010). X-ray computed microtomography: Distinguishing natural pearls from beaded and non-beaded cultured pearls. Gems & Gemology.
3. Gemological Institute of America (GIA). Pearl Research. Overview of traditional and modern gemmological methods for examining pearls.
https://www.gia.edu/pearl-research
4. Cartier, L. E. (2021). DNA fingerprinting and age dating of pearls and corals at SSEF. Facette 27, Swiss Gemmological Institute SSEF.
https://www.ssef.ch/dna-fingerprinting-and-age-dating-of-pearls-and-corals-at-ssef/
5. Swiss Gemmological Institute SSEF. Pearl Testing and About SSEF. The institute’s remit, scientific examination of pearls and explanations of laboratory reports.
https://www.ssef.ch/pearl-testing/
https://www.ssef.ch/about-ssef/
6. Ho, J. W. Y. & Shih, S. C. (2021). Pearl Classification: The GIA 7 Pearl Value Factors. Gems & Gemology, vol. 57, No. 2, pp. 135–137.
https://www.gia.edu/gems-gemology/summer-2021-pearl-classification-the-gia-7-pearl-value-factors
7. Swiss Gemmological Institute SSEF. Pearls – Understanding SSEF Reports. Definition of the weight units carat and pearl grain, and the examination criteria.
https://www.ssef.ch/reports/pearls/
8. Gemological Institute of America (GIA). Pearl Quality Factors. Principles for assessing size, shape, colour, lustre, surface quality, nacre quality and matching.
https://www.gia.edu/pearl-quality-factor
9. Gemological Institute of America (GIA) (2025). GIA 7 Pearl Value Factors: An Update on Nacre Classification. Gems & Gemology, Summer 2025.
10. CIBJO – The World Jewellery Confederation. CIBJO Guide for Classifying Natural Pearls and Cultured Pearls. Published by the CIBJO Pearl Commission, 2022.
https://cibjo.org/pearl-guide/
Further Specialist Reading
Gemological Institute of America (GIA). How GIA Identifies and Classifies Pearls. Description of laboratory procedures and examination methods.
https://www.gia.edu/gem-lab-how-gia-identifies-classifies-pearls
Swiss Gemmological Institute SSEF. DNA Fingerprinting. Information on identifying pearl-producing mollusc species using biological traces.
https://www.ssef.ch/dna-fingerprinting/
Gemmological Association of Great Britain (Gem-A) (2024). Why Does the Study of Gemmology Matter? Introduction to the scientific and practical importance of gemmology.
https://gem-a.com/gem-hub/why-does-the-study-of-gemmology-matter/