Conch
Pearls

Many kinds of molluscs can produce pearls. Pearls from the queen conch, S. gigas, are rare and have been collectors' items since Victorian times. Conch pearls occur in a range of hues, including white, brown, and orange, with many intermediate shades, but pink is the colour most associated with the conch pearl, such that these pearls are sometimes referred to simply as "pink pearls". In some gemological texts, non-nacreous gastropod pearls used to be referred to as "calcareous concretions" because they were porcellaneous (shiny and ceramic-like in appearance), rather than nacreous (with a pearly luster). The Gemological Institute of America and World Jewellery Confederation now use the simple term "pearl"—or, where appropriate, the more-descriptive term "non-nacreous pearl"—for such items, and, under Federal Trade Commission rules, various mollusk pearls may be referred to as "pearls" without qualification.

Although not nacreous, the surfaces of fine conch pearls have a unique appearance. The microstructure of conch pearls comprises partly aligned bundles of microcrystalline fibers that create a shimmering, slightly iridescent effect known as flame structure. The effect is a form of chatoyancy, caused by the interaction of light rays with the microcrystals in the pearl's surface, and it somewhat resembles moiré silk.
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