For the how long does it take for mussels to cook language, see Perl. The most valuable pearls occur spontaneously in the wild, but are extremely rare.

These wild pearls are referred to as natural pearls. Cultured or farmed pearls from pearl oysters and freshwater mussels make up the majority of those currently sold. Imitation pearls are also widely sold in inexpensive jewelry. Whether wild or cultured, gem-quality pearls are almost always nacreous and iridescent, like the interior of the shell that produces them.

Although these may also be legitimately referred to as “pearls” by gemological labs and also under U. The English word pearl comes from the French perle, originally from the Latin perna meaning leg, after the ham- or mutton leg-shaped bivalve. A black pearl and a shell of the black-lipped pearl oyster. The iridescent colors originate from nacre layers. All shelled mollusks can, by natural processes, produce some kind of “pearl” when an irritating microscopic object becomes trapped within its mantle folds, but the great majority of these “pearls” are not valued as gemstones. Cultured pearls are formed in pearl farms, using human intervention as well as natural processes.

The unique luster of pearls depends upon the reflection, refraction, and diffraction of light from the translucent layers. Because pearls are made primarily of calcium carbonate, they can be dissolved in vinegar. Calcium carbonate is susceptible to even a weak acid solution because the crystals react with the acetic acid in the vinegar to form calcium acetate and carbon dioxide. Freshwater and saltwater pearls may sometimes look quite similar, but they come from different sources. Freshwater pearls form in various species of freshwater mussels, family Unionidae, which live in lakes, rivers, ponds and other bodies of fresh water. Saltwater pearls grow within pearl oysters, family Pteriidae, which live in oceans. Saltwater pearl oysters are usually cultivated in protected lagoons or volcanic atolls.

Cross-section showing CaCO3 growth begins onto an organic center. Atomic-resolution image of atoms in nacre. Transition from spherulitic aragonite structures to nacre. Formation of nacre begins directly on massive aragonite. It is thought that natural pearls form under a set of accidental conditions when a microscopic intruder or parasite enters a bivalve mollusk and settles inside the shell.