How are pearls formed?

It is commonly believed that pearls are formed when a grain of sand enters an oyster; however, this has recently been disputed as a myth. While it is technically possible for a grain of sand to be at the center of a pearl, the oyster species that produce pearls are found on sandy ocean or freshwater floors and have the ability to expel sand and other objects like small pieces of seashells.

Did you know that the majority of natural pearls are formed in oysters as a response to a parasitic intruder? That’s right, a parasite! Parasitic organisms will burrow through the hard shell of an oyster and trigger its mantle (the inner tissue layer of an oyster) to secrete a barrier around the biological interloper. The parasite acts like a ‘splinter’ to the oyster.

A pearl is formed as a result and is covered with layers of nacre. Nacre is the iridescent layer of oyster shells that form pearls.