An “Eye” on a Tridacninae Pearl
The Tridacninae subfamily of giant saltwater clams consists of two genera: Hippopus and Tridacna. These bivalve mollusks live only in the shallow waters of coral reefs in the tropical parts of the Indo-Pacific Ocean (E. Strack, Pearls, Rühle-Diebener-Verlag, Stuttgart, 2001, p. 60). They are known to produce white to cream non-nacreous pearls, with yellow or orange pearls less commonly found. Tridacninae pearls frequently exhibit a porcelain-like surface with a flame structure caused by stacked layers of aragonite lamellae in a crisscross fashion. The sheen-like effect occurs when those lamellae interact with light (H.A. Hänni, “Explaining the flame structure of non-nacreous pearls,” Australian Gemmologist, Vol. 24, No. 4, 2010, pp. 85–88). Pearls with such characteristics are known as porcelaneous pearls.
A 4.77 ct near-round white Tridacninae pearl (see above) recently examined by the author displayed a well-arranged flame structure consisting of a wide base with spiky ends radiating outward from the apex of the pearl. Microscopic examination under fiber-optic light revealed a remarkable feature. A dramatic pseudo-chatoyancy occurred over the luminous flames, creating the appearance of an eye staring back at the observer. Pearls with prominent flame structures and high sheen often contain striking features.
