These pearls are gathered from freshwater lake and river mollusks. They can be mostly round to off-round, or rice-shaped to baroque. They look similar to Akoya pearls, but are the perfect gift when on a budget. They might be slightly less symmetrical, smaller, or not as easily matched, but these minor differences provide a major value for the price. The appealing, deep shine of a pearl is often what defines its beauty. This shine is produced by multiple layers of semi-opaque calcium carbonate crystals, called nacre. The nacre reflects light on the surface of the pearl, producing brilliance and sheen.