GIA Studies Non-Bead-Cultured Pearls from Pinctada margaritifera

Understand the challenge pearl testers face.

Gray to black pearls from the Pinctada margaritifera (black-lipped pearl oyster) bivalves are commonly referred to in the market as “Tahitian pearls” (figure 1). This name is almost always associated with cultured pearls (beaded and non-beaded). While gray to black are the most likely colors encountered, these pearls do exhibit a range that extends from light tones all the way to dark tones of gray to black. When their sometimes dramatic overtones—or mixes of other secondary hues—are included in the cocktail, their appearances can change dramatically, producing some very striking pearls that are in global demand. These overtones and/or secondary hues may be green, pink, purple, or a combination of colors leading to such exotic and descriptive terms as “Peacock,” “Aubergine,” or “Pistachio.” On rare occasions, white, brown, and yellow primary bodycolors with a range of overtones may also be found.

The Pinctada margaritifera mollusk’s habitat extends over a wide range but is most often associated with the Indo-Pacific region (Strack, 2006). The species almost always shows characteristic gray to black coloration over the mother-of-pearl that comprises the bulk of its body and which in turn is responsible via the genetics of its mantle for producing the recognizable color of Tahitian pearls. Nowadays the majority of Tahitian pearls produced commercially originate from French Polynesia (figure 2), a group of islands located in the south-central Pacific Ocean. Tahiti is the largest of the islands within the group and lends its name to the type of pearl under discussion.

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