Types of Pearls and Pearl Identification: An Australian Guide

What are the main types of pearls?

A pearl is a gem grown inside a living mollusc, usually an oyster or a freshwater mussel. Most pearls used in jewellery are made of nacre, the same iridescent material that lines the inside of the shell. Nacre is built from microscopic plates of aragonite (a crystal form of calcium carbonate) held together by conchiolin, an organic protein. Light travelling through thousands of these thin, overlapping layers is what gives a pearl its soft glow. If any term here is new, our plain-English jewellery glossary explains it.

Gemmologists sort pearls in three ways: by how they formed (natural or cultured), by where they grew (saltwater or freshwater) and by the species of mollusc that grew them. In practice, these are the types of pearls you will meet in Australian jewellery:

• Natural pearls: formed with no human help. Very rare today and found mostly in antique and estate jewellery.
• Akoya pearls: small, round, white saltwater cultured pearls, mainly from Japan and China; the classic strand.
• Freshwater pearls: cultured in mussels, mostly in China, with the widest range of shapes, colours and prices.
• Tahitian pearls: dark saltwater cultured pearls from French Polynesia, in greys, greens and peacock tones.
• South Sea pearls: the largest cultured pearls, white or silver from Australia and golden from the Philippines and Indonesia.
• Keshi pearls: solid-nacre pearls with no bead inside, formed as a by-product of culturing.
• Mabe pearls: dome-shaped blister pearls grown against the inside of the shell.

There are also non-nacreous pearls such as conch and melo pearls. They have a porcelain-like surface, often with a shimmering flame pattern, rather than the mirror-like lustre of nacre. They are rare collector's pieces. Pearl is also the traditional June birthstone, a month it shares with moonstone and alexandrite; see our June birthstone guide for all three. To see how each pearl type is used in strands, studs and pendants, visit our page on pearl jewellery and custom pearl designs.

What is the difference between natural and cultured pearls?

A natural pearl forms when something disturbs a mollusc's soft tissue, most often a parasite or an injury, and the animal seals it off with layer upon layer of nacre. The popular story about a grain of sand is largely a myth. Because it happens by chance, only a tiny fraction of wild molluscs ever contain a pearl, and very few of those are round or large. Most natural pearls sold today are older pieces, many from the historic Persian Gulf fisheries, and they need a laboratory report to confirm their origin.

A cultured pearl is still a real pearl, grown by a living mollusc, but a pearl farmer starts the process. In saltwater oysters a technician inserts a polished bead nucleus (a sphere usually cut from freshwater mussel shell) together with a small square of mantle tissue from a donor oyster. The tissue grows into a pearl sac around the bead and coats it in nacre. The oyster then goes back into the water for anywhere from under a year for some Akoya to two years or more for South Sea pearls.

Most freshwater pearls are grown differently: the technician inserts only pieces of tissue, with no bead, so the finished pearl is nacre almost all the way through. Cultured pearls are not imitations and they are not lab-grown; the pearl itself is formed entirely by the mollusc. Imitation pearls, by contrast, are not pearls at all. They are glass, plastic or shell beads with a pearly coating, sold under names such as faux, simulated or shell pearls. Our page on how natural and cultured pearls differ covers formation, history and value in more depth.

Which types of pearls grow in saltwater and which in freshwater?

The mollusc decides almost everything about a pearl: its possible size, its natural colours and how thick the nacre can grow. This table compares the main cultured types side by side, which is also the quickest way to start any pearl identification.

Akoya pearls are what most people picture when they think of a pearl strand: round, white and with a sharp, mirror-like lustre at a modest size. Freshwater cultured pearls cover the most ground. A single mussel can grow dozens of pearls at once, which is why they generally cost much less, and their solid nacre makes them durable. Top freshwater pearls can look very close to Akoya, though their lustre is usually softer and more satiny.

Tahitian black pearls get their dark colours naturally from the black-lip oyster. Truly black ones are uncommon; most are charcoal or grey with green, blue, pink or purple overtones, and a green-purple mix is called peacock. White and golden South Sea pearls come from the largest pearl oyster of all, and their size and thick nacre put them at the top of the cultured pearl price scale.

Mabe blister pearls are grown by attaching a half-bead to the inside of the shell. After harvest the dome is cut out, the half-bead removed, the space filled with resin and the back sealed with a piece of mother-of-pearl. Their flat backs suit earrings, rings and brooches, but the thin dome makes them more delicate than a whole pearl.

What makes Australian South Sea pearls from Broome different?

Australia is the leading source of white South Sea pearls. They grow in Pinctada maxima, the silver-lip pearl oyster, in the warm waters off Broome and the Kimberley coast in Western Australia and off the Northern Territory. Pinctada maxima is the largest pearl oyster, with a shell that can reach about 30 cm across, and that size is what lets it grow pearls of 10–15 mm and occasionally beyond 20 mm.

Broome has been a pearling town since the 1880s. The early luggers harvested wild oysters mainly for mother-of-pearl shell, used for buttons, with natural pearls an occasional bonus. Pearl culturing began in the region in the 1950s. The industry still relies heavily on wild oysters collected by divers under a managed quota, rather than only hatchery-bred stock. Australian South Sea pearls are typically white to silver with pink or silver overtones, and the oysters are usually left about two years before harvest, which builds a thick coat of nacre. Our page on Australian pearls from Broome covers the farms, the history and how they are graded.

After a first harvest, a healthy oyster can be seeded again, often with a larger bead. Some oysters reject the bead but keep growing nacre around the pearl sac, producing keshi. South Sea keshi are valued for their solid nacre, strong lustre and unique free-form shapes; our guide to keshi pearls explains how they form and what affects their value.

Comparing Akoya vs South Sea pearls shows how much the oyster matters. A fine Akoya is usually 6–8 mm with a thinner nacre coat and a crisp, bright lustre. A white South Sea pearl is often 10–15 mm with nacre many times thicker, giving a deeper, softer glow that looks almost lit from within.

What shapes and colours do pearls come in?

Pearl shapes are grouped into a few standard families. Round pearls are the rarest in every type, which is why a strand of well-matched rounds costs more than the same pearls in other shapes.

• Round: looks perfectly spherical to the eye and rolls straight.
• Near-round: very slightly flattened or elongated; hard to tell from round once strung.
• Oval: evenly elongated, like an egg.
• Button: flattened on one side; popular for studs because the flat side sits against the ear.
• Drop: teardrop or pear-shaped; used for pendants and drop earrings.
• Semi-baroque: slightly irregular, often with a gentle asymmetry.
• Baroque: clearly irregular and free-form; every one is different.
• Circled: any shape with concentric grooves or rings around it, common in Tahitian pearls.

Pearl colour has three parts. Body colour is the main colour you see, such as white, cream, gold or grey. Overtone is a translucent tint that seems to float over the surface, such as rose on a white Akoya or green on a Tahitian. Orient is a shimmer of rainbow colours that moves across the surface, seen mainly in pearls with thick, fine nacre and in keshi. Lustre, the sharpness of the reflections on the surface, matters more to beauty than any single colour. Our page on how lustre, nacre, surface, shape and size are graded explains each factor with examples.

Shape also decides how a pearl is worn. Buttons and near-rounds make practical studs, and pearl studs need a back that grips the post firmly; see which earring backs hold pearl studs securely. Baroque and circled pearls are increasingly worn by men too, in pendants, rings and pearl cufflinks, tie pins and other men's pieces.

How can you tell if pearls are real?

A few simple checks will separate most real pearls from imitations. They cannot tell a natural pearl from a cultured one; only laboratory testing can do that. Use several checks together, because a good imitation can pass one or two.

Be gentle with the tooth test; there is no need to bite, and a coated or polished pearl may feel smoother than expected. Shell-based imitations, made from beads of ground or solid shell with a pearly coating, are the most convincing because they feel heavy and cool. The drill hole is often the giveaway: under magnification an imitation's coating usually shows wear or a raised lip, while a pearl's nacre looks layered.

If a strand passes these checks, the next question is which type it is. Size, colour and lustre together narrow it down quickly: a 7 mm white round with sharp lustre is most likely Akoya or a fine freshwater pearl, a 12 mm silvery white pearl points to South Sea, and a dark 10 mm pearl with green overtones suggests Tahitian. Dark colour alone is not proof, though, because Akoya and freshwater pearls are often dyed black.

How do gemmologists identify natural, cultured and treated pearls?

Pearls are organic and built from layered aragonite, so many standard gem tests give vague results. A refractometer shows a broad, blurry reading of roughly 1.52–1.66, specific gravity sits around 2.60–2.85, and hardness is only about 2.5–4.5 on the Mohs scale. Laboratories rely instead on imaging and chemistry, the same scientific approach described in our scientific guide to gemstone identification.

• X-radiography and micro-CT: X-ray images show the inside of the pearl. A beaded cultured pearl shows a sharp boundary around a round shell bead; a natural pearl usually shows fine concentric growth rings; a tissue-grown cultured pearl often shows an irregular void or line at the centre. Micro-CT builds a 3D view for difficult cases.
• X-ray fluorescence: freshwater pearls contain more manganese and usually glow under X-rays, while most saltwater pearls stay dark. This is a key test for saltwater vs freshwater pearls.
• Trace-element analysis (EDXRF): measures elements such as manganese and strontium to help confirm the growing environment.
• UV fluorescence and spectroscopy: Raman and UV-visible spectra help separate natural colour from dye, for example a natural Tahitian from a dyed black Akoya or freshwater pearl.

Treatments are common and should always be disclosed. White pearls are often bleached to even out colour, and some are tinted pink. Dark colours can be produced by dyeing, by older silver nitrate treatment or by irradiation, which darkens the shell bead inside. Some pearls are polished or given a surface coating to boost lustre, which can wear off. A report from a recognised laboratory such as GIA will state whether a pearl is natural or cultured, saltwater or freshwater, and whether any colour treatment was detected.

What decides the value of each type of pearl?

GIA describes seven value factors for pearls. Other laboratories and farms use similar ideas, though there is no single worldwide grading scale:

• Size: measured in millimetres; within any type, larger pearls cost much more.
• Shape: round is rarest and most valued, then near-round, drop and button, then baroque.
• Colour: body colour, overtone and orient; preference varies by type and fashion.
• Lustre: how sharp and bright the reflections are; the most important beauty factor.
• Surface quality: the number and size of spots, bumps or pits.
• Nacre quality: thickness and fineness; thin nacre can look chalky and wear through.
• Matching: how well the pearls in a strand or pair suit one another.

Many sellers use letter scales. Akoya and freshwater pearls are often graded A to AAA, while Tahitian pearls commonly use A to D, where A is the top grade. Because these scales vary between sellers, ask which system is being used and compare pearls side by side rather than relying on letters.

These are broad ranges only; prices depend heavily on lustre, surface, nacre and matching, and they move with harvests and demand. Natural pearls are priced separately and can cost far more than cultured pearls of the same size, but only with a laboratory report confirming their origin.

How do you care for pearls and when should they be restrung?

Pearls are much softer than most gems and are sensitive to acids, so a little routine care goes a long way. Put them on last, after perfume, hairspray and make-up, and take them off first. Wipe them with a soft, slightly damp cloth after wearing to remove perspiration and skin oils. Keep them away from chlorine, vinegar and cleaning products, and never use ultrasonic or steam cleaners. Store them flat and apart from harder jewellery, which can scratch the nacre, and avoid sealing them in airtight plastic for long periods.

Strands are traditionally strung on silk with a small knot between each pearl, so that if the thread breaks only one pearl falls and the pearls do not rub together. Silk stretches and weakens with wear, so a strand worn often usually needs restringing every year or two. Signs it is time include gaps between the knots and pearls, a thread that looks grey or frayed, or a strand that hangs longer than it used to. GemTrove restrings pearls in-house; our page on pearl care and restringing explains what is involved.

How to identify a pearl: step by step

1. Look at the overall set. Note the size in millimetres, the shape and the body colour. These alone often point to one or two possible types.
2. Check the lustre and overtone. Sharp, mirror-like reflections suggest Akoya; a deep, soft glow on a large pearl suggests South Sea; a softer, satiny glow on a smaller pearl often suggests freshwater.
3. Do the tooth test gently. A slightly gritty feel suggests a real pearl; a smooth, glassy feel suggests an imitation.
4. Examine the drill holes with a 10× loupe. Look for layered nacre, a bead line or, in an imitation, chipped coating.
5. Compare the pearls on the strand. Small natural variations are normal; perfectly identical beads are a warning sign.
6. Ask about treatments. Dark pearls in particular may be dyed or irradiated, and white pearls are often bleached.
7. Get a laboratory report for valuable pieces. Only X-ray testing can prove a pearl is natural, and a report also confirms saltwater or freshwater origin.