Natural Spondylus (Thorny Oyster) Pearls

Thorny Oyster (Spondylus) Pearls

Thorny Oyster (Spondylus) Pearls

Non-nacreous conch, clam, Melo melo, Cassis, and scallop pearls are often submitted to GIA for identification. Four non-nacreous pearls, weighing 5.72 to 12.40 ct and measuring from 9.55 × 8.60 mm to 16.35 × 9.36 mm, were recently submitted to GIA’s New York laboratory for identification. These examples caught our attention because of their unusual appearance (figure 1).

Their bodycolors and shapes varied. Each exhibited some degree of pink and orange hues, and either elongated or button shapes. The porcelaneous surfaces also exhibited areas with clear flame structures. Under fiber-optic light, fine flame structures resembling those seen in other porcelaneous pearls such as Tridacna gigas and Strombus gigas (conch) pearls were observed. While the typical whitish flame structure was readily apparent, the more notable observation was that some of the flames had a distinct blue coloration (figure 2). Other types of pearls usually do not show blue flames. Microradiography was of little diagnostic assistance, as only tight structures were observed; this is not unusual for porcelaneous pearls. Raman spectroscopy detected both aragonite and calcite separately on different parts of the samples. In the authors’ experience, this differs from conch or clam pearls, which are usually composed of aragonite only.

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