Pearls are some of nature’s most beautiful creations, organic gemstones that have become a timeless staple in the jewelry industry. For centuries, pearls have been seen as a symbol of elegance and class. Unlike silver or gold, pearls are formed under water by mollusks such as oysters and mussels. Mollusks, belonging to the phylum Mollusca, have soft bodies covered in a mantle that helps produce the shell. Mollusks can ingest foreign objects such as grains of sand or pieces of shell while eating or during respiration. This object lodges itself in the mollusk’s mantle, irritating it. To protect itself from irritation, the mollusk emits nacre, an iridescent substance also known as mother of pearl. This substance coats the irritant. The process repeats over time, creating more and more layers, gradually forming the pearl. The number of layers determines the size of the pearl.

Pearls can either form naturally in the wild or are cultured with human assistance. Natural pearls are very rare and valuable, which is reflected in their high price. To produce cultured pearls farmers implant a nucleus into the mollusk, which is typically in the form of polished beads made from shells. The mollusk responds the same way it would to a natural irritant, covering it in layers of nacre over time. The process is started by humans, but finished naturally by the mollusk.

There are four different types of cultured pearls: Akoya, South Sea, Tahitian, and freshwater. Freshwater pearls are very common for jewelry due to their large range in size and color. As the name suggests, they are found in freshwater such as ponds and lakes. Akoya pearls are saltwater pearls that are also common in jewelry, most commonly white and cream in color. Tahitian pearls are found in saltwater surrounding the islands of French Polynesia. They are famous for their darker colors, including grey, black, and brown, with overtones such as pink, purple, and green. South sea pearls are found in salt water and are rarer than other pearls due to limited growing conditions which makes them more expensive. They are typically white, silver, and golden in color. 

A pearl’s value is typically based on luster, size, and color. Nacre plays a crucial role in determining these factors. Nacre, or mother of pearl, is made up of aragonite crystal layers separated by proteins from the mollusk’s shell. The thickness of each aragonite crystal layer determines how light reflects through the pearl, creating a distinct color. A pearl’s color has an extremely large range. To better control the color of cultured pearls, a method was created to record the average thickness of aragonite crystal layers in pearl farming. This method isn’t exact, but it does help predict and determine the color of cultured Akoya pearls. 

Pearls demonstrate how biological processes combined with time can turn a minor irritant into something incredible. From the gradual layering of nacre, to the wide variety of colors, pearls highlight the complex yet beautiful processes beneath the sea.