In July 2012, the New York laboratory received a most unusual pearl for examination. The 26.99 x 17.90 x 7.25 mm specimen bore
an uncanny likeness to a mushroom, consisting of a bell-shaped cap atop a narrower stem. In addition, under the cap we observed arching radial structures very reminiscent of the “gills” found in actual mushrooms. The pearl’s brown color further added to the mushroom effect.
After digital imaging, the pearl was examined with the microscope. It displayed a non-nacreous porcelaneous surface, with a noticeable flame structure at the top of the cap and a very subtle flame structure on the stem. The widest section of the pearl as well as the base of the stem showed a mottled growth pattern and coloration, which may have obfuscated any flame structure in those areas.
Microradiography revealed a denser growth structure along the center (lengthwise) of the pearl and visibly less compact layered growth in the widest area of the cap. This growth structure in the cap made it more fragile than the top and base of the pearl; minor fracturing and chipping were seen along the rim with the microscope, including a number of iridescent liquid-filled inclusions slightly below the surface.
Raman spectroscopy showed an aragonite peak, and EDXRF chemical analysis indicated the presence of Ca, as expected for a pearl. The absence of pigment/color concentrations indicated that the color was natural. The surface appearance, primarily the intersecting flame structure and liquid inclusions, pointed to a mollusk of the Cassis genus (i.e., a large marine snail). Although we had no way to confirm this through testing, the owner said it reportedly came from a Cassis cornuta mollusk found in the Indonesian archipelago.
While a pearl from a mollusk of the Cassis genus is uncommon in its own right, the shape of this specimen is what made it truly remarkable. Its striking resemblance to a mushroom has not been observed by GIA in any other pearl, from any mollusk species.
Image: This 26.99 x 17.90 x 7.25 mm pearl has a unique mushroom shape (top, photo by Jian Xin (Jae) Liao). It displays a subtle flame structure on the stem (bottom, photomicrograph by A. Hyatt; image width ~7 mm).
Courtesy of GIA (Gemological Institute of America) © 2012.