P earls are biogenic gem materials that may form naturally without human intervention, or with assistance from humans in a culturing process. Natural and cultured pearls often display similar external appearances and occasionally cannot be differentiated without examining their internal structures. Over the last century, scientists and gemological laboratories have used film X-radiography and digital real-time microradiography (RTX) to reveal these interior growth patterns (

No abstract

No abstract

No abstract

Pinctada maxima (the silver-or 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