While both natural pearls and cultured pearls are real, their creation is the biggest difference between them. Natural pearls occur in clams and oysters when an irritant, like a grain of sand, gets inside the creatures' shells. For protection, the bivalve coats it with nacre, a form of calcium carbonate. The nacre protects the clam from the intruder and forms layers over time, creating a natural pearl inside the shell.
Pearl farmers deliberately insert seeds, which are small beads or rounded pieces of clam shells, into clam shells' bivalves to force the creation of pearls. The cultivation process requires one to two years to produce a market-worthy pearl. By contrast, natural pearls take many years to grow to desirable sizes and can cost up to 10 times more than their cultured cousins.
When inspected, natural pearls have onion-like layers caused by slow growth. Cultured pearls do not have this layering, due to their rapid growth. Jewelers often use this absence of layers to differentiate natural pearls from cultured pearls.
Pearl farmers are capable of mass-producing pearls with consistent quality and color at a lower cost for jewelers and consumers when compared to natural pearls. Natural pearls still carry great prestige in the jewelry industry, but their price tags make them less popular on the casual consumer market.