Technically, the term for this naturally occurring, iridescent organic composite is “nacre,” but it has long been called “mother of pearl.” Nacre is secreted by specialized cells in the mantle tissue of certain species of salt- or fresh-water molluscs and is continuously deposited onto the inner surface of the animal’s shell. The nacreous layer is actually a defense against parasitic organisms, but this inner shell layer is very attractive and often beautifully colored, making it highly valued as jewelry or as inlays in wood furniture and musical instruments. When a mollusc with a nacreous layer is invaded by a parasite or irritated by a foreign object (a grain of sand, for instance), the animal secretes successive, concentric layers of nacre, which over time form what we call a pearl. Pacific pearl oysters have successfully been aquicultured for generations for their iridescent nacre, as well as being “seeded” to produce pearls. Those little sea creatures go to a lot of effort to make the inlay on your guitar look nice, don’t they….