The Creation of a Pearl

• A pearl forms when an irritant, such as a particle of food, becomes trapped inside the body of a mollusk. The mollusk secretes layers of nacre around the irritant to protect itself, forming the body of the pearl.
  
  

Nacreous and Non-Nacreous Pearls

• It's the reflective aragonite in nacre that gives pearls their prized luster. Some pearls form with the aragonite arranged in pointed needles, instead of flat sheets; these pearl have no luster, and are called non-nacreous pearls.
  
  

Natural and Cultivated Pearls

• Naturally produced pearls are exceedingly rare, occurring only in one out of every 10,000 or so mollusks. In the late 1800s, a number of entrepreneurs learned how to stimulate mollusks to produce pearls, and the cultivated pearl industry was born.
  
  

Types of Pearls

• Both freshwater and marine mollusks produce pearls. Unless you have very specific knowledge of the "look" of pearls, it would be difficult to tell the two apart.
  
  

Pearl Variations

• Pearls vary in size, shape and color depending on many factors, including the type of mollusk, the shape of the irritant that stimulated the pearl, even the temperature of the water.