Pearls are objects produced within the soft mantle of a mollusk. Like the shell of the mollusk, a pearl is composed of a microcrystalline calcium carbonate that is deposited in thin concentric layers.
Pearls can occur spontaneously in nature, but the bulk of the world’s pearls are obtained through farming, or culturing, pearls from freshwater mollusks. Wild pearls, or pearls occurring without human intervention, are incredibly rare.
“Seeding” a pearl means inserting a bead of a predetermined shape and size into the tissue of a mollusk in order to control the shape of the pearl. The most valuable shape in the gem trade is a perfectly spherical pearl. A baroque pearl, meaning misshapen, is seeded from the natural contours of the mollusk’s mantle. In contrast to a round pearl, baroque pearls are valued for their individuality.
Other qualities that affect the value of a pearl are color and luster. Pearls will naturally occur in white, pale pink, and black. In order to be considered a gem grade Pearl, it must demonstrate iridescence over its entire body and the color must have good surface luster.
Author Fred Ward notes that pearls were most certainly the world’s first valued gemstone, needing no cutting or polishing. Unlike other stones with one or few sources, pearls occur indigenously all around the globe.