Natural pearls grow naturally in oysters living at sea without human intervention. When any irritant or a parasite enters inside an oyster or mollusk the process of natural coating begins with layer upon layer of nacre inside the oyster.Natural pearls are rarely found now-a-days and as a result cultured pearls are very real and genuine. Cultured pearls are formed by human intervention when a nucleus is implanted inside the oyster and the coating process  begins with layers upon layers of an iridescent substance called nacre. This process takes approx. 2-5 years to form a complete pearl depending upon techniques and where it is grown, sea or rivers among other conditions. Reflection and refraction from the translucent layers truly determines the unique luster quality of pearls. The display of iridescence in pearls is the  result of overlapping the successive layers.
All the pearls found and sold in the market today are cultured pearls, whether fresh water or seawater pearls. Fresh water pearls are generally grown in ponds, lakes or rivers whereas seawater pearls are grown in the sea  Whether fresh water or sea water pearls, quality and price depends upon the size, shape, lustre, color and surface.