Natural Pearls 

  • How did pearls become important to the world’s gem market?
  • What are the two main types of natural pearls?
  • What are the characteristics of natural abalone pearls?
  • What mollusks produce non-nacreous natural pearls?

The history of natural pearls goes back thousands of years. They adorned kings, queens, and nobles. They motivated explorers and conquerors, kept thousands of people employed, and supported the entire economies of some countries.

Many natural pearls sold today are the very same pearls collected and cherished in past centuries. Some have grown in value with age. At a 2008 auction in Dubai, United Arab Emirates, Christie’s—the London-based auction house—sold a natural pearl and diamond necklace for more than $1.7 million. Another natural pearl necklace brought just under $1.4 million. And a single large freshwater natural pearl sold for $713,000.

Today, cultured pearls have displaced natural pearls as the centerpiece of the global pearl trade. Natural pearls are still harvested—most often as byproducts of gathering wild mollusks for food—but the quantity and overall market values are a tiny fraction of what they once were.

The earliest natural pearls to be harvested and widely sold were natural blister pearls, which form over an irritant on the inside of a mollusk’s shell. They look like bumps adhering to the shell.

Natural pearls consist of nacreous and non-nacreous varieties. To be nacreous, they must meet two criteria. First, they must be composed wholly or principally of aragonite. Second, the aragonite platelets and conchiolin must be arranged in concentric layers that are mostly parallel to the pearl’s surface.

Each aragonite crystal is between 0.2 and 0.6 micron thick. A micron is about one-fiftieth the thickness of a human hair. Under very high magnification, the arrangement resembles a wall built of aragonite “bricks” and conchiolin “mortar.” Because of their composition and construction, nacreous natural pearls generally display higher luster than non-nacreous natural pearls.