Internal Structures of Known Pinctada Maxima Pearls: Cultured Pearls from Operated Marine Mollusks

GEMS & GEMOLOGY FALL 2021 P inctada maxima (the silveror gold-lipped pearl oyster), Pinctada margaritifera (the blacklipped pearl oyster), and Pinctada fucata (martensii) (“the akoya pearl oyster”) are the main mollusks of the Pinctada genus that are commercially farmed. They are routinely used to produce bead cultured (BC) pearls and, as a consequence, sometimes also produce non-bead cultured (NBC) pearls (Otter et al., 2014; Sturman et al., 2016; Nilpetploy et al., 2018a). P. maxima is the largest species in the genus (Scarratt et al., 2012) and generally requires a minimum two-year growth period to yield BC pearls with the thickest nacre layers of all BC pearls (Gervis and Sims, 1992; Cartier and Krzemnicki, 2016). Cultured pearls from the P. maxima mollusk are often referred to as “South Sea” in the market. Australia is the largest producer of white P. maxima (silver-lipped) cultured pearls, while Indonesia, Myanmar, and the Philippines are major producers of “golden” P. maxima (gold-lipped) cultured pearls. The farms producing these pearls are located between the Tropic of Cancer and the Tropic of Capricorn, which coincides with the native P. maxima mollusk’s geographic distribution. The silver-lipped shells are found mostly south of the equator, while the gold-lipped shells populate the region north of the equator (Strack, 2006). P. maxima mollusks used for pearl culturing production in Australia are predominantly wildcaught shells collected in accordance with the annual quota that takes the shell sizes into account (between 120 and 175 mm shell length) and allows fishing INTERNAL STRUCTURES OF KNOWN PINCTADA MAXIMA PEARLS: CULTURED PEARLS FROM OPERATED MARINE MOLLUSKS