Two Large Natural Pearls Reportedly from Spondylus and Trochoidea Species Mollusks
In a Fall 2014 Lab Note (pp. 241–242), GIA reported on four natural pearls ranging from 5.72 to 12.40 ct that were reportedly from a Spondylus (thorny oyster) species. These interesting non-nacreous pearls showed porcelaneous surfaces with unique bluish flame structures. Another even larger natural pearl, also reportedly from a Spondylus species, was recently submitted to the New York laboratory for identification. This pearl measured approximately 24 × 16 mm and weighed 42.96 ct (figure 1, left). It was formed in an attractive drop shape with a homogeneous yellow-brown bodycolor, abundant surface grooves, and a distinct bluish flame structure (figure 2). As with previous examples, microradiography showed only a tight structure, lacking obvious growth arcs. In addition, aragonite and natural polyenic pigment peaks were detected by Raman spectroscopy. Its unique appearance, coloration, and bluish tinted flame structures consistent with Spondylus pearls we previously reported. There is no known cultured pearl from this species, and the tight structure is commonly seen in other non-nacreous pearls, which further confirmed its natural origin.
The same client also submitted a large natural nacreous pearl reportedly from an unknown Trochoidea (turban snail) species (figure 1, right). The specimen, which measured approximately 27 × 19 × 12 mm and weighed 39.30 ct, had a cream color, high luster, and strong orient. Its smooth surface showed a unique wavy pattern. Previously GIA reported on a natural pearl from the turban snail species Astraea undosa that also showed high luster and strong iridescent colors, with an undulating wave-like pattern (Winter 2003 GNI, pp. 332–334). Both pearls share many common characteristics, and their appearances closely resemble one another.
Our client claimed that the Spondylus pearl is from Baja, Mexico; the turban pearl is from Mexico’s Pacific coast. Although it is extremely challenging to identify the exact mollusk species these rare pearls originated from, their unique and interesting appearances are consistent with previously studied materials of similar claims. Regardless of their exact origin, these beautiful large natural pearls prove just how wonderful Mother Nature is at creating spectacular wonders of great variety and eye-pleasing form.