What are pearls? Unlike gemstones produced deep inside the Earth, pearls are created by living creatures called mollusks. Mollusks commonly have a soft, unsegmented body and a hard exterior shell, such as a clam or snail has. These animals live in marine and freshwater habitats as well as on land. The evolutionary history of this group extends back some 530 million years, with approximately 100,000 species of mollusks alive today. Any mollusk that produces a shell can produce a pearl. Nevertheless, naturally occurring pearls are rare, found in perhaps one of every 10,000 animals. The cultured pearl industry, which has flourished since the early 20th century, has developed techniques to greatly improve these odds. Indeed, more pearls are produced now than at any time in human history. Imitation Pearls Because pearls are so rare, people have for thousands of years created substitutes for the real thing. Records indicate that the ancient Romans made imitation pearls. And Queen Elizabeth I of England, whose passion for pearls is apparent in every portrait of her, is said to have established an artificial pearl industry to supply what nature could not. The techniques for manufacturing imitation pearls have varied over the centuries and today include coating glass beads with a mixture of varnish and fish scales or flakes of the mineral mica.