Lab Notes Gems & Gemology, Spring 2015, Vol. 51, No. 1

Conservation Concerns over Use of Tridacna Shell in Imitation Pearls

White shell bead
Figure 1. Left: This white shell bead (10.08 mm) was visible after the coating was removed from one of the imitation pearls. Right: A subtle flame structure was observed on the surface of the shell bead; magnified 40×. Photos by Jessie Yixin Zhou.
Last year the New York laboratory reported on the use of shell as a pearl imitation (Summer 2014 Lab Notes, pp. 153–154) and the improper nomenclature applied by those marketing it. We decided to delve deeper and investigate the nature of the shell beads used in such imitation pearls following correspondence with Dr. Henry A. Hänni, who previously reported on this issue (see Summer 2004 Gem News International, p. 178, and references within).

After removing the outer coating on one of the imitation pearls by immersing it in acetone, we observed a banded white bead (figure 1, left). Magnification revealed fine and subtle flame structures (figure 1, right), indicating the bead was most likely fashioned from the shell of a Tridacna (giant clam) species.

All species of the Tridacnidae family are currently listed in Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Some species, such as Tridacna gigas, are more vulnerable than others, such as Tridacna squamosa or Tridacna maxima. These large saltwater clams can have heavy shells fluted with multiple folds (figure 2) and colorful mantles. Their natural habitats lie in the warm marine waters of the Indo-Pacific, a fragile region that has been heavily impacted by human activities.

Tridacna shells
Figure 2. These three shells of Tridacna species are part of the collection at GIA’s Bangkok laboratory. The two largest measure approximately 33 × 20 cm each. The two larger shells were found empty by Thai divers, while the smaller shell was donated to the Bangkok lab several years ago and comes from an unknown source. Photo by Nuttapol Kitdee.
These beautiful marine animals are commonly harvested from their natural habitats or aquaculture farms for food (Center for Tropical and Subtropical Aquaculture Publication No. 114, University of Hawaii), and their shells are fashioned into beads or ornaments that are prized by some cultures. Despite their protection under CITES, these shell products are readily available on the Internet and often very inexpensive (figure 3). Imitation shell “pearls” fashioned from these endangered and protected mollusks do not offer any obvious advantages over common freshwater mussel shells, and it is extremely difficult to identify the exact Tridacna species or whether the mollusks were farmed or harvested from the wild. We urge manufacturers to stop using Tridacna shell beads when producing imitation pearls.

Tridacna shell beads
Figure 3. Tridacna shell beads of various sizes (4.5 to 10.5 mm) are readily available from various commercial sites. The carved beads shown on the left are marketed as “Tibetan prayer beads.” Photo by Sood Oil (Judy) Chia.

Jessie Yixin Zhou is a staff gemologist, and Chunhui Zhou is research scientist and supervisor of pearl identification, at GIA’s New York laboratory.