Real, or genuine, pearls can be either saltwater or freshwater, natural or cultured - nearly all pearls marketed today are cultured.

Basically, a cultured pearl is created when a farmed oyster is deliberately implanted with an irritant, often a tiny bead made from mussel shell. This causes the oyster to coat the irritant with a lovely iridescent substance called nacre, commonly known as Mother of Pearl. 

Natural pearls are harvested from oysters in the open seas. Also the result of reacting to an irritant, these pearls form without any human intervention or oversight. Finding and harvesting wild oysters is risky and highly regulated, hence their increasing rarity and cost. 

Natural freshwater pearls, however, are much more common, but as their popularity grows, so do freshwater oyster farms and pearl culturing to meet the demand.

Saltwater pearls come from oysters native to oceans and seas. All such pearls are exports from Japan, China, Indonesia, French Polynesia, Australia and other, typically tropical, locales. The only pearl oyster in the Americas is found in the Sea of Cortez and is considered among the most beautiful and valuable of all the pearls.

Freshwater pearls come from mussels native to rivers and streams and are the "new kids" in the cultured pearl realm. Their incredible variety of shapes, sizes, colors, luster, and affordability have skyrocketed sales - and understandably so!