Freshwater and saltwater pearls differ in terms of luster, durability, size and way of growing the pearls. Freshwater pearls have a softer, less glossy luster, while saltwater pearls have a brilliant and superficial luster. Freshwater pearls are generally more durable because they have much thicker nacre than saltwater pearls.
The nucleus piece inserted in freshwater water pearls is small, and this makes the resulting pearl piece almost entirely made of nacre. Usually, it takes four to six years to grow freshwater pearls, while saltwater pearls take six to 18 months to grow. These are the reasons why saltwater pearls have thinner nacre coating and are smaller in size. Freshwater pearls grow in a variety of shapes unlike saltwater pearls which are round.