A Pearl Primer

Nancy LT Hamilton.

Last updated:  11/15/20, 3/25/20, 5/26/17, 3/17/17.

Still under construction as of 11/15/20.

Subscribe to my newsletter and see my Pearl edition, Volume 15 for more information!  Newsletter signup is on the right side of my home page.  Thanks!

This page is more about pearls than it is about grading, buying, and testing.  I’m working on a page that talks about these things but, it could take a while!


What is a Pearl?

  Un-technically, a pearl is a hard,  rounded, but not round, shiny thingy that grows within the shell of a mollusk (Mollusca). The pearl is coated with a product, that the mollusk makes in its mantle, called “nacre”. The mollusks can be pearl oysters, triangular oysters, mussels, abalone – any mollusk that has a shell. Mollusks can also be found in saltwater or freshwater or on land and are either univalve (abalone), gastropods (snails), or bivalve (Oyster, mussel, clam).  Cephalopods, like the squid and octopus, do not produce pearls although, they are in the mollusk phylum.  There are over 50,000 know species of the phylum “Mollusca” of which 9,200 (living species) are bivalves.

Essentially, if you’re a mollusk and you have a shell, you can produce a pearl!

  Abalone (univalve) Shell.     Oyster (bivalve) Shell.

Pearls DO NOT start with a grain of sand.  Sand has never been found in the nucleus of a pearl.   If pearls had sand as a nucleus, you can bet that every mollusk would contain pearls – many, many pearls – and their lives would be scratchy and uncomfortable.   See this video that shows how a mollusk removes sand from its body. Warning:  it involves mucous!

Interesting Things About Mollusks and Pearls

  • Most mollusks have no eyes or only simple eyes that are photosensitive and possess a simple lens.  The cephalopods are the exception here.  All mollusks have photosensitive receptors to detect shadows. They can also have sensors that detect pressure (mechanoreceptors) and some can detect chemical substances that induce a biological signal (Chemoreceptor).
  • Many types of Mollusca change sex.   Most start life as males and then change to females.  Some change back to male, if there are ladies present. “The Sex Life of a Mollusk”, below.
  • Abalone cannot be used for cultured pearl production because they are hemophiliacs.  Their bodies are incapable of clotting and any puncture or laceration will kill them.
  • Cephalopods have less than a thousand species to their credit. That sounds like a lot until you realize that there are 50-80,000 alive today.  (My research indicates that not everyone agrees on one number with reputable sources stating different amounts.) The cephalopods are a much more complex branch of the mollusk’s tree with complex eyes, feet, and brains, are much more mobile, are larger and a lot more intelligent than their mollusk cousins, like the clam, abalone or oyster. Some, like the octopus, might give us a run for our intellectual money.
  •   Cephalopod means: “head-foot”.  Just look at an octopus to understand that name!  Image credit:  Hyperactivez.com
  • Less than half of the millions of oysters implanted, survive.  Of the survivors, only 5% will produce high-quality pearls.
  • Several species of Mollusk have extraordinary lifespans!  The Geoduck can live for over 160 years, the Freshwater Pearl Mussel 190 years and the winner of the longest lifespan is the Ocean Quohog at over 400 years!   Credit:  Hans Hillewaert/Wiki Commons/CC License
  •  Artificial nacre has been created in the laboratory.

Pearls: Natural and Cultivated

The first classification of pearls is whether they are Natural or Cultivated.  Next, there are 4  main types of pearls: freshwater pearls, Akoya pearls, South Sea pearls (white and golden), and Tahitian pearls. Sub-types are  Round and Baroque Pearls.  Round pearls are considered traditional pearls and every other shape is considered Baroque.  But, under the heading of Baroque, are a ton of different shapes.  See my Google Sheets page:  Pearls: Types, Locations, and Characteristics.  The chart breaks down pearls clearly and simply, so you can easily tell the difference between them.  Take a copy of it with you to your next gem show foray!

Natural Pearls

          A natural pearl is simply a response, by the mollusk, to a foreign body, damage, or disease.  Examples of occurrences that can cause pearls to form are a parasite, like a sea worm, an autoimmune disease, or some form of damage to the shell.   Many natural pearls grow as a result of tapeworm larvae, inadvertently being filtered.  The larvae, common in sharks, fish, and rays, enters the mollusk.  As it tries to escape, it drags epithelial cells along with it – sealing its fate.  The epithelial cells (in the mantle) deposit layer, upon layer of calcium carbonate over the, now dead body, of the tapeworm larvae, creating a worm-shaped pearl. This layer of calcium carbonate and chitin is called nacre (pronounced: NAY-ker).

A pearl can form when an oyster is injured – by a fish bite, getting stepped on, falling rocks, etc.  A bit of the shell protrudes gets dislodged into the mantle.

Once an invader – either a piece of shell, a parasite, or other disruptive elements,  enters the mantle area, the mantle produces a substance called nacre (nacre is only present in saltwater pearl oysters, freshwater pearl oysters, and abalone.).  The mantle applies layer after layer onto the intruder and continues covering it with nacre.  The nacre protects the mollusk against further damage and smooths and rounds the foreign material.

Many natural pearls began life as tapeworm larvae.  The tapeworms are present in the surrounding waters, coming from sharks, manta rays, and fish (makes you want to keep your mouth tightly closed while swimming!).  The mollusk, while filtering the surrounding waters, will inadvertently bring the larvae into its body.

Sometimes, a mollusk will develop an autoimmune disease or other physical disorder. Following is a quote from Dave LeBlanc at Lagoon Island Pearls, on the various issues the poor mollusk may face (he is, specifically, discussing a mussel that contained a thousand pearls but, the disorders apply to some natural pearl production):

“a blood-borne condition. Hormonal disorders, blood acid/base imbalance or protozoan (or other organisms) infection can cause pearls to form”.

To read Dave’s awesome response on pearl-guide.com, click here.

  The insides of a natural pearl.  The nacre builds up, over the irritant, layer by layer, creating a tree ring-type interior.

Natural pearls are EXTREMELY rare nowadays.  1 in 10,000 wild mollusks will produce a pearl, according to the National Geographic Society’s post. But, the International Gem Society notes that: “only one in several million shellfish ever yield[s] a pearl.”  Raw Pearls.com.au (Australia) notes: “Only 1 in about 10,000 wild oysters will yield a pearl and of those, only a small percentage achieve the size, shape, and colour (sic) desirable to the jewellery (sic) industry.”  So, who knows.  Let’s just say that all the pearls, that (maybe) you or I can afford or will encounter are not natural pearls.  Usually, natural pearls are found in estate jewelry, private collections, and museums.

With the advent of cultured pearls, the natural pearl industry plummeted.  Suddenly, pearls were inexpensive and plentiful.

 Abalone with a “worm pearl”.  Credit:  The Trustees of the British Museum.

Cultured Pearls

The second type of pearl is the cultured pearl.  A cultured pearl is simply one wherein a nucleus, of various materials, is inserted into the sexual organ of the mollusk (the gonad), by a human.  Instead of layer upon layer of nacre, starting at the core, the cultured pearl’s nacre develops over the nucleus – creating a pearl within a year or two.

You can’t tell a natural pearl from a cultured pearl unless you look inside.  Some use X-rays to see whether a pearl is natural or cultured. If a pearl is already drilled. Small, fiber optic light allows the inspection of the interior of the pearl.


Oysters are ready for nucleating when they are mature generally around  1-3 years old. The implantation process is performed by highly trained surgeons on anesthetized mollusks. They need to be quick as the mollusk can become dehydrated and die. The surgeons insert the tissue and nucleus into the mantle of the mollusk.

Harvesting Pearls

Not all oysters or mussels are killed when the pearl is harvested.  But, Some, like the Pteria Sterna oyster raised in the Sea of Cortez, is harvested towards the end of its lifecycle- at about 5 years. The harvesting process kills them. Other pearls are carefully removed in delicate surgery.

4 Basic Types of Pearl


South Sea – White & Golden

  Wild South Sea oyster.

These pearls are highly valued. Their color range is white to golden.  White pearls generally come from the northwest coast of Australia while the golden pearls hail from the Philippines and Indonesia.

Many of the south sea oysters from Australia are wild with supplemental bred oysters added to the mix.  The oysters from the Philippines and Indonesia are mostly hatchery-bred.  This mixing of wild and bred oysters introduces new genetic diversity to keep the stock healthy.

   Range of Golden South Sea Pearls.  Image Credit:  Pure Pearls.

 Credit:  PearlParadise.com

Due to the longevity of the south sea oyster (up to 40 years), they can produce very large, lustrous pearls.  The nacre is made up of very large aragonite crystals and on average, their nacre is the thickest of all pearls. The oyster is bead nucleated.

The white South Sea pearl’s growth period is usually 2-4 years with pearls reaching sizes of 8 – 20 mm.  12 mm is the average size.  Only 10% – 30% of each harvest is round or near-round.  The mollusk is the silver-lipped Pinctada Maxima.

  White South Sea pearl shapes. Image credit:  Pearl Paradise.



Baroque Pearl Types




Coin Pearls



Flame Pearls

Keishi Pearls

Keishi pearls are created when the bivalve rejects the implanted nucleus or if the mantle breaks and forms additional pearl sacs. There, an unnucleated pearl can develop.

Most Keishi pearls come from pearl farms.  Since the cause, for the formation of the keishi pearl, is difficult to ascertain, they are considered cultured pearls.

A keishi pearl can be a natural pearl but, the geographic location and/or the type of mollusk should be indicated to clarify the type of pearl that it is.

Keishi pearls, generally, have a high luster due to the fact that they are solid nacre.


Peanut or Twin



Mollusks are invertebrates – meaning they lack a spine.  Invertebrates make up 97% of the animal kingdom, so watch out – they’re taking over (or already have taken over!). One of the reasons that there are so many invertebrates is because they are quite fast at reproducing.

A mollusk has four  (or 5 depending on what type of mollusk we are talking about) basic body divisions:  a head, a foot, a shell, a mantle, and a visceral mass.  (I have one of those, I think!)

  • The head contains sense organs and the brain.
  • The foot is a muscle that helps the mollusk to hold on to and/or move through its environs. With a mollusk, like a squid, the foot has evolved into tentacles and arms used for locomotion and food gathering. Both the octopus and the squid belong to the sub-group cephalopods.
  • The mantle produces the shell. Once again, the squid and the octopus have to be different!  They have an internal shell to which their muscles attach to.
  • The shell offers protection. But, not all mollusks have shells – think slugs!
  • The visceral mass consists of the internal organs such as the digestive and reproductive systems, respiratory systems, and excretory systems, etc.

Anatomy of a Mollusk

Nacre/Mother of Pearl

 Abalone    Black Lipped (Rainbow)

  Akoya    Gold Lipped

Nacre is the same material that creates the inside and the outside of the shell as well as the material that coats pearls.  Mother-of-pearl (the inside of the shell) is made from nacre also.

Nacre is composed of flat platelets of calcium carbonate crystals that are stacked in alternating, brick-like layers that are about 300-500 nanometers thick.  The crystals are coated with and surrounded by a protein called “chitin” and a silk fibroin–like protein that is water-insoluble.

The chemical composition of nacre, for those that care, is 82-86% calcium carbonate (CaC03), 10-14% chitin, and 2-4% water.

Not all the nacre found in mollusks has the same crystalline structure.  Some, like the Windowpane Oyster, produce elongated, hexagonal crystals.

BTW, the color of the oyster’s lip (mantle) influences the color of the pearl.

  Nacre.  Note the calcium carbonate layers. Credit: Fabian Heinemann/Wikipedia

  In 2009, researchers have discovered two proteins that create a nacre.  They are called: Pif 80 and Pif 97.   These two proteins were reduced by 40%, from oysters and the oysters barely produced any nacre. The nacre became abnormal, microscopically It became apparent that these proteins were necessary for the production of nacre. The Pif 97 creates the framework and describes how the nacre looks with the chitin.  “Pif 80 binds calcium and bicarbonate to the chitin, finishing the nacre.” * 2. NS (see Nacre Resources).

The hope is that is the reduction of these two proteins can almost stop the production of nacre, that the opposite would also prove true:  increase the proteins and create pearls faster.

Nacre, due to its structure can prevent a crack, in the oyster’s shell, from reaching the interior organs.  The crystalline “bricks” slide over one another and the chitin stretches a little.  The force driving the crack is rerouted, into the alternating layers of calcium carbonate crystals and chitin and is diffused.  Nacre’s slightly wavy structure and its ability to divert stresses not only protects the oyster from attack or accident but, also gives the shell great flexibility and strength.  Scientists at Cambridge University have succeeded in creating a synthetic nacre that has great future potential – perhaps in the coatings industries or in the production of uncrackable ceramics – not to mention a non-lethal way to obtain pearls and mother of pearl!

The Sex  Life of a Mollusk

Some Mollusca change sex.  Those that do, start life as a male and change into a female again.  This gender-swapping is based on environmental changes, nutritional and other stresses.  Some species alternate seasonally or when there is a change is water temperature.

Mollusks may have sex at a very young age; some are able to reproduce in their first year!  Others aren’t sexually mature until three (no judgment!).

To spawn, a mollusk needs to have enough energy (don’t we all!) to be able to grow a gonad.  This gonad will either produce sperm or an egg.

  Supper for a mollusk (phytoplankton).  Credit:  Samantha DeCuollo, University of Rhode Island

Warmer water, salinity changes, food availability (phytoplankton) can signal the ocean-living mollusk to start making the gonad.  The process of growing the gonad takes about 2 months. Finally, when the water temperature and the salinity levels are just right, the romance begins.  The mollusks release, either their sperm or their eggs, nilly willy,  into the sea.  Nearby mollusks, filtering in their neighbor’s gametes, sense that something fun is afoot and enthusiastically join in.  One randy mollusk can start a spawning orgy in the neighborhood!

The eggs and sperm run into one another, in the water’s currents, and continue the process of making baby mollusks. These little guys are called Veligers.

Once fertilized, the eggs drift off, swimming, vertically (they can only swim vertically) through the water, in search of tasty phytoplanktons!  They will drift and swim about for two weeks, or so.  By this time, they will have developed a foot (pediveliger stage).  Next comes the search for a suitable home.  Once they find the mollusk loft of their dreams, they secrete a glue, that keeps them firmly planted for the rest of their lives. (Ah, now I understand why the parents release them, alone and tiny, into the big, bad, sea.  If raised at home, they’d never leave!).

  Oyster spat on an oyster shell.  Credit: Ladon Swann.

Once home, they begin a complete, internal metamorphosis.  At this stage, the larva is called a “spat”. The little spat will grab calcium carbonate, from the surrounding waters, and collect it to form a shell.  The amount of time that the mollusk remains a spat, depends on the type of mollusk – 1-3 years generally.

At maturity, the process begins anew.

The History of the Pearl

Supposedly, the Chinese in the 13th century were the first to create cultured pearls. These were not the almost round pearls of the 1900s but, blister pearls; seeded with mud, bone, metal, or other objects. There are nacre covered objects dating to the

Purportedly, Carolus Linnaeus (1707-78), was experimenting with creating cultured pearls.  Using limestone and metal, he implanted the irritant into the oysters.  Six years later, he found a mediocre pearl.

One of the world’s major suppliers of natural pearls, for thousands of years, was the Arabian Sea. Pearls were harvested around the Persian/Arabian Gulf and the Red Sea as well as in the Gulf of Manaar between India and Ceylon.

During those thousands of years, when the Persian Gulf was the principal supplier of pearls, divers, and pullers were the workhorses of the industry.

Pearls were harvested from ships called Dhows.  Pearl dhows would have 40 -50 people onboard. Besides the captain, ship’s boys, cooks, and sailors, there would be divers and pullers.

  To collect the oysters, the divers and pullers worked as a team.  Two ropes were used:  one rope had a heavy stone tied to the end and a loop was made in it.  The diver put his foot into the loop and stood on the stone.  The other rope was tied to the diver’s waist and was his link to the surface.

The puller would drop the diver and the ropes, over the side of the dhow and the stone would carry the diver to the bottom.  Next, the puller would yank up the rope with the stone and the diver would get to work collecting, as many oysters as he could, on one breath.

The diver wore a nose clip (often made from tortoiseshell) and finger sheaths, on one hand, for protection.  He also carried a bag or a basket to hold his catch in.

The life of a diver was a perilous one.  Some of the hazards a diver faced were:  chronic conjunctivitis (that could cause blindness), punctured eardrums (which could cause deafness), ruptured blood vessels, and living threats such as stonefish, stingrays, and sharks – to name a few!  But, the job was prestigious due to its inherent danger and the bravery required.

The pearls were graded, usually on land,  by pearl merchants who would classify and value them so that the fishermen could get paid.

The pearl merchants carried with them specialized tools, called Dastas, for grading pearls.  The merchant would grade the pearls for luster, color, size, and shape.  The tools of a pearl merchant’s trade were:  a red cloth, to aid in inspection, scales, to weigh the pearls and sieves, for sorting them into their various sizes.  The merchants used elaborate calculations to determine value, based on the weight of the pearl.

The Romans adored pearls too and highly valued them.  They were a sign of wealth and prestige.

Pearls and Europeans

Europeans purchased their pearls from merchants that traded along the southern and eastern Mediterranean.

Around 1498, the Portuguese found a route to Asia:  the Cape of Good Hope (at the tip of Africa).  Once that route was discovered, it wasn’t long before the Portuguese had taken control of the pearl industry.  They didn’t bother with controlling the fishermen but instead,  imposed taxes on the fishing boats and on their sales.

Christopher Columbus, during his third and fourth voyages to the New World, encountered pearls in what would become Venezuela and Panama.  Hernán Cortés discovered new sources in the Bay of California.  Discoveries of pearls were made in many South American locales such as Panama, Mexico, and Honduras.

Pearls were also found, during the 1700s, in the south seas, by European explorers who, of course, brought about a demand for the spectacular South Sea pearl.

  (Credit: The Sun).   Because of their scarcity, naturally occurring pearls will cost much more than cultured pearls. In fact, they can cost more than diamonds! Recently, a single pearl sold for (well, it was EXTRAORDINARY!)  Made by a giant clam (in the Philippines), it weighs 75 lbs. and measures 26″ X12″ AND it sold for $100,000,000.

The whole story of the cultured pearl is confusing and complicated.  I’m assuming that many were playing with the process and that they were aware of one another’s experimentation.  There’s always that drive to be the FIRST.  So, it’s rather difficult to describe.

Basically, several different people were working on creating cultured pearls at one time.

William Saville-Kent, a British ex-pat, living in Australia, was, according to C. Denis George the first to develop the process.  You can read George’s argument in the article below (under Resources):  Debunking a Widely Held Japanese Myth.

At the same time that Saville-Kent was working on the process, three men (and a woman) from Japan:  Kokichi Mikimoto and his wife and business partner, Ume – experimental pearl farmers and business people, Tokichi Nishikawa – scientist, and Tatsuki Mise – carpenter, were also exploring the production of cultured pearls

Kokichi Mikimoto purchased oyster farms with the hope of creating pearls.  He and his wife finally succeeded in producing cultured, 1/2 pearls (Blister or Mabe pearls) in 1893.  It wasn’t until 1905 that they were able to produce spherical pearls. Mikimoto’s method involved placing a bead of calcium carbonate into the oyster’s shell.

Pinctada Maxima

 Silver-lipped or Pinctada Maxima oyster shell.  Image credit:  Australian South Sea Pearls.

  Image credit:  Pearl Classic.

Farming of Pinctada Maxima oysters started in the late 1800s.  But, they weren’t widely distributed until the 1950s.

Wild Pinctada Maxima are mainly found in the area along 80 Mile Beach, in Western Australia (in the NW of the country).  But, oysters are farmed all along the northern coast.

The city of Broome, in the northwest corner of Australia, was (in the early 1900s) and still is, the commercial center for the white-lipped oyster’s pearls.


The next defining categories for a pearl are whether it is a fresh or a saltwater mollusk.

Saltwater Pearls

Raised in Salt Water.  Typically,

Freshwater Pearls

Resources and Research Sources

History Sources

Mollusca (Mollusk) Sources

  • MolluscaBase (2018). Accessed at http://www.molluscabase.org Date sourced:  5/26/18. Database of molluscan species.
  • Bunje, Paul. “The Mollusca“.  University of California Museum of Anthropology. (2003) http://www.ucmp.berkeley.edu/taxa/inverts/mollusca/mollusca.php.  Date sourced:  5/26/18.
  • Oysters Life Cycle.”.  Horn Point Lab Oyster Hatchery.
  • The Sex Life of Oysters“. Chris Lim. The Watershed Project. 4/5/12. http://thewatershedproject.org/the-sex-life-of-oysters-how-olympia-oysters-reproduce-under-the-bays-warm-waters/.  Date sourced:  5/26/18.

Nacre Sources

  • Berkely Lab.  Mother of Pearl Secret Revealed.  11/25/08.  http://newscenter.lbl.gov/2008/11/25/mother-of-pearl-secret-revealed/.  Sourced:  5/28/18.
  • 2.NS. Bland, Eric. Science on NBCNews.com. Proteins That Make Pearls Shimmer Are Found. 08/14/09.  Sourced: 05/28/18.
  • The University of Cambridge Research. 7/4/12. Scientists Create Artificial Mother-Of-Pearl.  http://www.cam.ac.uk/research/news/scientists-create-artificial-mother-of-pearl.  Date sourced: 5/28/18.

Pearl Sources