Conch Pearl, Strombus gigas or "Queen Conch", Caribbean Sea. Photo Bonhams.

A conch is one of a number of different species of medium-sized to large saltwater snails and their shells. True conchs are marine gastropod mollusks in the family Strombidae, and the most well known species is the "Strombus gigas or "Queen Conch". The pearls they produce are calcareous concretions—that is they are non-nacreous and are made up of calcium carbonate (rather than aragonite which is the composition of nacreous pearls).

Several thousand snails would have to be found in order to recover a pearl as fine—and as large—as this one. Of ovoid form, with deep rose color, the present lustrous pearl has an excellent flame pattern iridescence. Weighing 7.70 carats and measuring 11.5 x 9.2 x 7.5mm. Sold for US$ 10,625 (€7,941)

Bonhams. Gems, Minerals and Lapidary Works of Art New York - 23 May 2012