There are two main types of pearls; natural and cultured. Almost all pearls on the market are cultured. Pearls are cultured in either freshwater or saltwater. Although these pearls share the same chemical composition, saltwater pearls tend to cost more because their production is smaller and the cost of production is higher. However, with freshwater pearls, the range in quality and price covers a larger spectrum because freshwater pearls are by far the most widely produced in the industry.
There are three main types of saltwater pearls: Akoya, South Sea, and Tahitian pearls. Akoya pearls used to be the go-to pearls for the classic strand of pearls because of their high luster, beautiful color, smaller size and accessible price. Freshwater pearls have created a large competition for these pearls. South Sea Pearl oysters can grow as large as a dinner plate, which in turn makes for rather large pearls. They are, on average, 13mm in diameter and are known for their satiny luster, thick nacre and soft colors. Tahitian pearls are known for their dark color, which can range from purple to greenish hues.
Large pearls are always more expensive than a similar, smaller pearl because they take longer to form. Due to the rarity of perfectly round pearls, they are by far the most valuable shape of a cultured pearl. Pearls with high luster and a smooth surface are also among the more desirable value factors.-Written by Mark Andrew Scales, Graduate Gemologist GIA