More on the pearl one of my favs…
Pearls are one of the only gemstones made by living creatures. Mollusks produce pearls by depositing layers of calcium carbonate around microscopic irritants—usually a grain of sand, as it’s commonly believed—that get lodged in their shells.
While any shelled mollusk can technically make a pearl, only two groups of bivalve mollusks (or clams) use mother-of-pearl to create the iridescent “nacreous” pearls that are valued in jewelry. These rare gemstones don’t require any polishing to reveal their natural luster.
Appropriately, the name “pearl” comes from the Old French perle, from the Latin perna meaning “leg,” referencing the leg-of-mutton shape of an open mollusk shell. Because perfectly round, smooth, natural pearls are so uncommon, the word “pearl” can refer to anything rare and valuable.
The rarest and most expensive pearls are natural pearls made in the wild without human interference. The majority of pearls sold today are cultured or farmed by implanting a grafted piece of shell (and sometimes a round bead) into pearl oysters or freshwater pearl mussels.