The Gemological Characteristics of Pipi Pearls Reportedly from Pinctada Maculata

Abstract

I n the Polynesian language, pipi means "small" or "tiny" and is used to refer to the small, predominantly yellow or "golden" pearls that originate from the bivalve mollusk Pinctada maculata (Gould, 1846). As the smallest mollusk species in the Pinctada genus, Pinctada maculata rarely exceeds 5 cm when measured in the anterioposterior or dorsoventral positions. The mollusk lives in the Indo-Pacific Ocean, mostly around French Polynesia and the Cook Islands, where they are often found in association with the Pinctada margaritifera mollusk species (Strack, 2006). Pearls from Pinctada maculata often form in round to near-round shapes. As the name implies, the small shells produce small pearls that rarely exceed 8 mm in diameter (Krzemnicki, 2014). Based on GIA's experience, 6 mm or under is more typical of the species. Pipi pearls are known to occur as natural pearls rather than cultured and, compared with other Pinctada species, are deemed rare. One report recorded only one gem-quality pearl found from a total of 355 mollusks (Passfield, 1997). In 1950, several cultured pearl experiments using Pinctada maculata reportedly took place but were unsuccessful (Segura et al., 2014). In the late 1990s, a few Pinctada maculata cultured blister pearls resulted from experiments in the waters off Penrhyn, an island in the northern atoll of the Cook Islands (Kessrapong et al., 2017). The nacre covering the bead nuclei did not fully overgrow the nuclei, however, and this attempt was not very successful. Some reports suggest that the Pinctada maculata mollusk is not abundant enough for commercial exploitation. Local regulations also protect them from being harvested by foreigners, further limiting the chances of cultured pearl production (Buscher, 1999). Given the limited documentation of Pinctada maculata cultured pearls, it is almost certain that all pearls currently fished from the species are natural pearls.

Internal Structures of Known Pinctada Maxima Pearls: Natural Pearls from Wild Marine Mollucks

“…This observation is also consistent with the majority of natural pearls tested in all GIA's pearl testing locations. Tight or minimal growth structure is commonly observed in natural pearls produced by many mollusk species of both nacreous and non-nacreous pearls (Krzemnicki et al, 2010;Scarratt et al, 2012;Karampelas, 2017;Nilpetploy et al, 2018b;Scarratt and Hänni, 2004;Wing Yan Ho and Zhou, 2014;Wing Yan Ho, 2015;Wing Yan Ho and Yazawa, 2017).…”

“…Irregular dense core structures have only been observed in natural pearls, in the authors' experience, and have not been reported in any NBC pearls. However, an off-round feature associated with the main core in sample 3-5 looks suspicious and could be construed as being a light gray CaCO 3 "seed" feature sometimes found in NBC pearls (Krzemnicki et al, 2010(Krzemnicki et al, , 2011Nilpetploy et al, 2018a;. Thus, if this pearl was tested without any supporting provenance, it could be interpreted as being NBC.…”

“…Moreover, the central feature within the core has a linear form, and such features have been observed in NBC pearls produced by various mollusk species. Similar linear features, although not exactly the same, are often considered sufficient evidence to classify pearls as NBC (Hänni, 2006;Sturman, 2009;Krzemnicki et al, 2010;Sturman et al, 2016;Nilpetploy et al, 2018a;Manustrong, 2018). RTX and μ-CT imaging of samples 2-14 and 2-15 showed patchy concentric structures that appeared neither light nor dark gray, and these were due in part to differences in the organic content within the areas.…”

“…The position of the pearl in the mollusk is indicated by a black arrow. (Wehrmeister et al, 2008;Sturman, 2009;Krzemnicki et al, 2010;Otter et al, 2014;Sturman et al, 2016;Nilpetploy et al, 2018a;Manustrong, 2018;Al-Alawi et al, 2020). In many cases, voids are a key identification feature by which to differentiate NBC from natural pearls.…”

“…Owing to the different appearances of both types of formation, they are separated into different groups in this article. Linear structures have been regarded as characteristic of NBC pearls from both saltwater and freshwater environments (Scarratt et al, 2000;Sturman, 2009;Krzemnicki et al, 2010;Sturman et al, 2016;Nilpetploy et al, 2018a;Manustrong, 2018;Al-Alawi et al, 2020). Interestingly, 5 of the 774 natural pearl samples also displayed linear structures (table 7).…”