A Non-Nacreous Pearl Reportedly from Telescopium telescopium
GIA’s Bangkok laboratory recently examined a yellowish brown and black non-nacreous button-shape pearl weighing 1.72 ct and measuring 6.64 × 6.53 × 5.07 mm. The pearl exhibited an attractive porcelain-like luster.
The client informed GIA that the pearl was found in a Telescopium telescopium shell. This edible snail (N. George et al., “DNA barcoding of gastropod Telescopium telescopium (Linnaeus, 1758) found at the Karachi coast, Pakistan,” Journal of Animal and Plant Sciences, Vol. 31, No. 5, 2021, pp. 1530–1536) was retrieved from an abandoned shrimp pond near a mangrove forest in Krabi, Thailand. The story of the pearl’s discovery was widely publicized in the local media. Though the client was unable to submit the shell from which the pearl was extracted, they provided us with samples of the same type of shell for further study (figure 1).
Observation through a 10× loupe and a microscope revealed long cracks traversing the darker side of the pearl (figure 2A). No polishing lines or evidence of surface or color modification were observed, indicating that the shape and color were natural. The pearl and shells exhibited flame structures similar to those routinely observed in pearls such as those from the horse conch (Summer 2018 Lab Notes, pp. 211–212). Intersecting and overlapping flame structures typically observed in pearls from the Cassis genus (Fall 2012 Lab Notes, pp. 211–212) were also detected on the pearl (figure 2B) and shells (figure 2C). However, the banded structure observed on the cut shells (figure 2D) was not visible on the pearl, additional evidence that the client’s item was a pearl and not an imitation fashioned from shell.
Real-time microradiography confirmed a natural whole pearl, as growth arcs close to the center and surface-reaching cracks were revealed (figure 3). As expected, energy-dispersive X-ray fluorescence analysis detected calcium as a major component in the pearl and shells, while manganese levels of less than 15 ppm and strontium levels ranging from 1005 to 2675 ppm verified a saltwater formation environment. The pearl’s natural color was substantiated using additional advanced spectroscopic methods. Raman spectra collected using a 514 nm argon ion laser on the pearl and shells (figure 4) revealed peaks related to the vibration modes of aragonite at 703, 1085, and 1464 cm–1; polyenic-related peaks at 1017, 1105–1120, 1297, and 1490–1500 cm–1 (S. Karampelas et al., “Polyacetylenic pigments found in pearls and corals,” 30th International Gemmological Conference, Moscow, 2007; L. Bergamonti et al., “The nature of the pigments in corals and pearls: A contribution from Raman spectroscopy,” Spectroscopy Letters, Vol. 44, No. 7-8, 2011, pp. 453–458); and an additional peak at 1175 cm–1 that is also likely related to polyene.
Surface observations and data collected from the pearl and shells using analytical methods appeared to support the claim that the pearl formed in this mollusk species. However, this can only be confirmed by conducting DNA barcoding analysis, which is a destructive test. This report adds to the growing list of natural pearls found in edible oysters and snails described in the literature (e.g., Winter 1995 Gem News, pp. 280–281; K. Scarratt et al., “A note on a pearl attached to the interior of Crassostrea virginica (Gmelin, 1791) (an edible oyster, common names, American or Eastern oyster),” Journal of Gemmology, Vol. 30, No. 1-2, 2006, pp. 43–50; Fall 2019 Gem News International, pp. 439–440; Fall 2020 Lab Notes, pp. 420–422; Summer 2021 Lab Notes, pp. 152–153). However, this is the first time a natural pearl has reportedly been discovered in a Telescopium species. Its unique appearance and characteristics provided a rare opportunity for GIA gemologists to examine and record data from a natural pearl originating from this marine snail.
