Unusual Melo imitation
In May 2008, a large "Melo pearl" weighing 66.30 ct was submitted to the lab (Fig. 1). The pearl showed the flame structure as seen in natural melo pearls. However, there was also visible banding, as seen in shell material, and some orange color concentration along some of these bands (Fig. 2). No polish marks were seen that would suggest it was a worked material. The pearl was almost round, with a diameter varying between 20.19 and 20.80 mm.
Melo pearls come from the Melo melo marine snail, which is found in the waters of the South China Sea, as far south as Singapore and west as the Andaman Sea. Like conch pearls, the melo gem is not actually a nacreous pearl because it contains no nacre. Like the better known pink conch pearls, melos are non-nacreous and show a distinct flame structure. Just like in coral, the orange color is derived from carotene.
The pearl submitted to the laboratory matched the color of a melo pearl, but the banding was suspicious, being unlike anything we had previously encountered in a natural melo pearl. A Raman spectrum was taken and compared to the Raman spectrum of a paler melo melo shell. While the pale yellow shell showed clear carotene peaks, the much more saturated pearl was lacking these peaks (Fig. 3).
With the lack of natural color, plus the banding not seen in natural melo pearls, we concluded that this must have been cut out of a shell. The only one that could give such a big diameter and at the same time exposing flame structure is the giant clam, Tridacna gigas, which can reach up to four feet in diameter. Giant clams are white in color, hence the specimen we had was dyed to imitate a melo pearl.
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| Fig. 1: This "melo pearl", weighing 66.30 ct with a diameter of over 20 mm, was submitted to the laboratory for testing. |
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| Fig. 2: A closeup of the surface shows flame structure, interrupted by repeated banding. Orange color concentration is found in the banding. |
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| Fig. 3: Raman spectrum of a melo melo shell (bottom). Besides the aragonite peaks at approx. 1088, 707, and 210 cm-1, some additional carotene peaks at 1530 and 1138 cm-1 can be seen. These are lacking in the spectrum of the melo imitation (top). |
