A unique necklace containing 63 pearls of various colors, shapes, sizes and mollusk species (Pteria and Pinctada species, and Pinnidae family) was recently submitted to the Carlsbad laboratory for examination (figure 1). Ranging in size from 4.88 mm to 10.75 × 9.32 mm, all the pearls were nacreous and exhibited overlapping aragonite platelets under high magnification, and the majority displayed a pronounced orient or iridescence phenomenon.
Interestingly, several pearls displayed similar crosslines with various surface patterns, seen in figure 1. The crosslines appeared to be natural grooves with no signs of surface treatment. Further testing identified these as Pteria pearls.
Nine pearls of light yellowish brown to brown colors displayed a similar linear-looking nacre appearance caused by slender rectangular aragonite platelets, which has been observed on the nacreous surface of Pinna or pen pearls belonging to the Pinnidae family (figure 2; E. Strack, Pearls, Rühle-Diebener-Verlag, Stuttgart, Germany, 2006; N. Sturman et al., “Observations on pearls reportedly from the Pinnidae family (pen pearls),” Fall 2014 G&G, pp. 202–215). The nacre of pearls from the Pteria and Pinctada species generally consists of hexagonal or polygonal aragonite platelets.
Under long-wave ultraviolet radiation, many of the pearls exhibited weak to strong orangy red to red fluorescence, which is characteristic of the porphyrin pigment found in colored Pteria pearls (figure 3; L. Kiefert et al., “Cultured pearls from the Gulf of California, Mexico,” Spring 2004 G&G, pp. 26–38). The fluorescence intensity of the Pteria pearls varied depending on their darkness and color saturation. The samples with more intense colors displayed a stronger red reaction. In contrast, darker pearls from the Pinctada species exhibited weaker green to greenish yellow reactions. The pen pearls showed a weak to moderate chalky yellow fluorescence, consistent with the reaction of some pen pearls (Sturman et al., 2014).
Real-time X-ray microradiography (RTX) revealed various growth patterns of natural pearls. Many Pteria samples contained a typical large dark gray organic-rich area in the center, and a faint radial structure was also present within the dark area in some samples (figure 4). One pen sample exhibited an irregular dark gray void associated with light gray granular features that was previously observed in some natural nacreous pen pearls (Sturman et al., 2014) and in GIA’s research collection.
Energy-dispersive X-ray fluorescence (EDXRF), ultraviolet/visible reflectance spectroscopy, and photoluminescence spectroscopy using a 514 nm laser excitation analyses indicated that all the pearls were of saltwater origin and naturally colored.
The client who submitted the necklace noted that the pearls were reportedly fished from the coastlines of the Mexican state of Baja California Sur, from both the Pacific Ocean and the Gulf of California (Sea of Cortez), over the course of eight years. The Pteria pearls were fished near San Carlos and Guerrero Negro, the pen pearls from the San Ignacio lagoon and Muleje, and the Pinctada pearls from Loreto. Based on the geographical information provided and the gemological characteristics observed, the mollusk species can be more precisely determined. The Pteria and Pinctada pearls likely came from Pteria sterna and Pinctada mazatlanica, respectively, as both species are indigenous along Mexico’s Pacific coast and the Gulf of California (M. Cariño and M. Monteforte, “History of pearling in La Paz Bay, South Baja California,” Summer 1995 G&G, pp. 88–105; Strack, 2006). Although the Pinnidae family is widespread globally, pen pearls from Atrina tuberculosa (often called Atrina maura) are local to Mexico and noted to produce pearls with a partially nacreous surface (Strack, 2006).
Mexico has been a rich source of pearls since ancient times (Cariño and Monteforte, 1995). Overfishing, changes in water environment, and dam construction have shortened the lifespan of indigenous mollusks and limited pearl production since the end of the nineteenth century (D. McLaurin-Moreno, “Sea of Cortez pearls: A historical overview,” Sixteenth Annual Sinkankas Symposium—Pearl, Gemological Society of San Diego and GIA, pp. 6–29). These new pearls from native species signal the return of healthy mollusk beds.
A unique necklace containing 63 pearls of various colors, shapes, sizes and mollusk species (Pteria and Pinctada species, and Pinnidae family) was recently submitted to the Carlsbad laboratory for examination (figure 1). Ranging in size from 4.88 mm to 10.75 × 9.32 mm, all the pearls were nacreous and exhibited overlapping aragonite platelets under high magnification, and the majority displayed a pronounced orient or iridescence phenomenon.
Interestingly, several pearls displayed similar crosslines with various surface patterns, seen in figure 1. The crosslines appeared to be natural grooves with no signs of surface treatment. Further testing identified these as Pteria pearls.
Nine pearls of light yellowish brown to brown colors displayed a similar linear-looking nacre appearance caused by slender rectangular aragonite platelets, which has been observed on the nacreous surface of Pinna or pen pearls belonging to the Pinnidae family (figure 2; E. Strack, Pearls, Rühle-Diebener-Verlag, Stuttgart, Germany, 2006; N. Sturman et al., “Observations on pearls reportedly from the Pinnidae family (pen pearls),” Fall 2014 G&G, pp. 202–215). The nacre of pearls from the Pteria and Pinctada species generally consists of hexagonal or polygonal aragonite platelets.
Under long-wave ultraviolet radiation, many of the pearls exhibited weak to strong orangy red to red fluorescence, which is characteristic of the porphyrin pigment found in colored Pteria pearls (figure 3; L. Kiefert et al., “Cultured pearls from the Gulf of California, Mexico,” Spring 2004 G&G, pp. 26–38). The fluorescence intensity of the Pteria pearls varied depending on their darkness and color saturation. The samples with more intense colors displayed a stronger red reaction. In contrast, darker pearls from the Pinctada species exhibited weaker green to greenish yellow reactions. The pen pearls showed a weak to moderate chalky yellow fluorescence, consistent with the reaction of some pen pearls (Sturman et al., 2014).
Real-time X-ray microradiography (RTX) revealed various growth patterns of natural pearls. Many Pteria samples contained a typical large dark gray organic-rich area in the center, and a faint radial structure was also present within the dark area in some samples (figure 4). One pen sample exhibited an irregular dark gray void associated with light gray granular features that was previously observed in some natural nacreous pen pearls (Sturman et al., 2014) and in GIA’s research collection.
Energy-dispersive X-ray fluorescence (EDXRF), ultraviolet/visible reflectance spectroscopy, and photoluminescence spectroscopy using a 514 nm laser excitation analyses indicated that all the pearls were of saltwater origin and naturally colored.
The client who submitted the necklace noted that the pearls were reportedly fished from the coastlines of the Mexican state of Baja California Sur, from both the Pacific Ocean and the Gulf of California (Sea of Cortez), over the course of eight years. The Pteria pearls were fished near San Carlos and Guerrero Negro, the pen pearls from the San Ignacio lagoon and Muleje, and the Pinctada pearls from Loreto. Based on the geographical information provided and the gemological characteristics observed, the mollusk species can be more precisely determined. The Pteria and Pinctada pearls likely came from Pteria sterna and Pinctada mazatlanica, respectively, as both species are indigenous along Mexico’s Pacific coast and the Gulf of California (M. Cariño and M. Monteforte, “History of pearling in La Paz Bay, South Baja California,” Summer 1995 G&G, pp. 88–105; Strack, 2006). Although the Pinnidae family is widespread globally, pen pearls from Atrina tuberculosa (often called Atrina maura) are local to Mexico and noted to produce pearls with a partially nacreous surface (Strack, 2006).
Mexico has been a rich source of pearls since ancient times (Cariño and Monteforte, 1995). Overfishing, changes in water environment, and dam construction have shortened the lifespan of indigenous mollusks and limited pearl production since the end of the nineteenth century (D. McLaurin-Moreno, “Sea of Cortez pearls: A historical overview,” Sixteenth Annual Sinkankas Symposium—Pearl, Gemological Society of San Diego and GIA, pp. 6–29). These new pearls from native species signal the return of healthy mollusk beds.
