A pearl forms when an irritant works its way into a particular species of oyster, mussel, or clam. As a defense mechanism, the mollusk secretes a fluid to coat the irritant. Layer upon layer of this coating is deposited on the irritant until a lustrous pearl is formed. The process of producing a pearl can range from six months to several years. Even before this, it takes about three years for the mollusk to reach a mature age in order to produce a pearl. A mollusk is only able to begin the pearl making process naturally or with the help of humans when it reaches this mature age.
Naturally occurring “black pearls” are even more rare. They are largely considered the most beautiful kinds of pearls in the world. Pearls that are identified as “black” are actually charcoal grey, silver, or dark green, and found almost exclusively in Tahiti.
If only my boogers were as valuable. Happy hunting and oh yeah, "Gesundheit!"