Large Natural Fossil Blister Pearls - article by GIA

Fossil pearls, first mentioned in 1723 in John Woodward’s “An essay towards a natural history of the earth and terrestrial bodies,” were described in greater detail by R. Bullen Newton in 1908 (“Fossil pearl-growths,” Journal of Molluscan Studies, Vol. 8, pp. 318–320). It is a rare occurrence to receive such pearls at GIA, which is why two large fossil blister pearls recently submitted to the New York laboratory immediately caught our attention.

According to the client, the pair of fossil blister pearls were found near Lunga Lunga, a region in southeastern Kenya bordering Tanzania. They were found attached to a fossilized giant clam shell that weighed approximately 297 kg and was discovered 4.3 meters below ground (figure 1) along with some fossilized corals. The shell, along with the attached pearls, was presented to the client as a gift from a local Digo tribe. It took a month to remove the entire shell from the ground. Similar fossilized giant clam shells have been recovered from areas along the Kenyan coastline (G. Accordi et al., “The raised coral reef complex of the Kenyan coast: Tridacna gigas U-series dates and geological implications,” Journal of African Earth Sciences, Vol. 58, No. 10, 2010, pp. 97–114). These two blister pearls were subsequently removed from the shell and submitted to GIA for identification after cleaning and removing the outermost fossilized debris.

The blister pearls measured approximately 58 × 47 × 45 mm and 85 × 70 × 46 mm and weighed 758 ct and 1256 ct, respectively. The faces of these pearls had a porcelaneous appearance and were smoother than the bases, which were attached to the clam shell. These bases showed chalky rough surfaces and flared forms (figure 2). Numerous natural indentations and cavities were present on their surfaces. In some areas, subtle flame-like structures were also observed at 10× magnification with the use of fiber-optic lighting (figure 3).

Read entire article here: http://www.gia.edu/gems-gemology/winter-2015-labnotes-large-natural-fossil-blister-pearls-tridacna-species

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