How are pearls formed

Do you love pearls, their look, and beauty? Have you ever looked at a pearl ornament and wondered how it was harvested? Most people think pearls are made in laboratories or factories. However, they are not far from the truth. There are three different types of pearls; natural, cultured and imitation. Most of the pearls we see around are the cultured and imitation types. The natural pearls are more expensive and rare.

Pearls can be described are a shining hard object found in the living tissue of mollusks such as oysters and mussels. It is the only gemstone found in a living creature. Pearls have been adorned for centuries and are highly sought after. They come in different shapes, sizes, and colors. Over the years, round and white pearls have been the most sought-after pearls. Pearls often come with a distinctive glow derived from a fluid, nacre secreted by mollusk which gives it an exquisite beauty.

Types of pearls

Pearls come in three types based on their mode of formation. They are;

  • Natural Pearls
  • Cultured Pearls
  • Imitation Pearls

Pearls can also be categorized based on their sources. They include;

  • Saltwater Pearls
  • Freshwater Pearls

How are Pearls Formed?

Natural Pearls Formation

Natural pearls are made inside living creatures such as mollusk and mussels. Natural pearls can be made from any type of mollusk and mussels. Other animals that produce pearls are abalones, conchs, pen shells, and whelks. Mussels that produce pearls are known as pearl mussels. Pearls are formed when an irritant such as parasite, sand, food or parts of the mollusk mantle become trapped in the mollusk’s body. These particles or organism gain entry into the mollusk body when its shell valves are open for respiration or feeding.  To protect itself from the irritant and prevent damage to its tissue, the mollusk sets up a defense mechanism by secreting a mixture of aragonite (a mineral) and conchiolin (a protein) on the irritant to create a pearl sac. This mixture known as the nacre is also what the mollusk uses to create its shell. As the mollusk secretes more layers of nacre on the irritant, the layers grow bigger and form the pearl with the irritant serving as the nucleus.

Cultured Pearls Formtaion?

Cultured pearls are pearls that are farmed from pearl oyster and freshwater mussels. There are two types of cultured pearls;

  • Beaded cultured pearls
  • non-beaded freshwater cultured pearls

Beaded cultured pearls are produced by surgically implanting a nucleus bead from a freshwater mussel shell and a small piece of tissue from another mollusk into the gonad (reproductive organ) of the mollusk. The pearls are produced one pearl at a time and are usually harvested between 2 – 3 years. Examples of the beaded cultured mollusk are Akoya, South Sea, Tahiti, and modern big freshwater pearls.

Non-beaded freshwater cultured pearls are produced by implanting graft (up to 25) on each wing of the mollusk. This process produces more pearls than the beaded cultured pearls. It is also more widespread although pearls produced through this process are low quality compared to beaded cultured pearls. Examples of non-beaded freshwater cultured pearls are Biwa or Chinese pearls.

Imitation Pearls Formation 

Imitation pearls are pearls made from mother-of-pearl, coral or conch shells or from glass coated with a solution of fish scales known as essence d'Orient. Imitation pearls typically have poor iridescence and are inexpensive. They are also characterized by their weight and smoothness which are different from natural pearls.

Shapes, color, and size of pearls

Pearls come in various shapes, sizes and color that enables it to be distinguished from each other. It shapes ranges from round, semi-round, button, drop, pear, oval, baroque, circled to double bouldered. Pearls that are round are the most valuable however they are rare. Button pearls are flattened pearls and can be used as earrings. Pearls can be seen in colors such as pink, blue, champagne, green, black and purple. However black and white saltwater pearls are the most popular. The standard unit of measurement of a pearl is the momme.

I momme = 3.75 gram.

How to identify natural, cultured and imitation pearls

While one can distinguish pearls by their look, shape, and weight, the best way to determine the type of pearl is by carrying out x-ray examination of the pearl in a lab. For imitation pearls, one can easily identify it by robbing it across the teeth. Imitation pearls glide easily across the teeth while real pearls feel gritty.


X-Ray Result

Type of Pearl

Nucleus is present

bead-nucleated saltwater pearl

No nucleus is present, but irregular and small dark inner spots indicating a cavity are visible, combined with concentric rings of organic substance

Cultured freshwater pearl

Shows larger cavities where organic matter has dried out and decomposed.

Natural pearls


There are no doubts that pearls have shaped the beauty industries for many years and a good understanding of its formation may lead to more appreciation for these gemstones.


Written by Olanrewaju Arilomo

Older Post Newer Post

Leave a Comment

Please note, comments must be approved before they are published