A pearl is a hard, shiny ball of crystalized calcium carbonate. Pearls are grown in living shell mollusks, mostly oysters.
A pearl is formed in a shell mollusk as part of its defense mechanism. When a foreign substance enters the shell, the animal covers this with layers to protect itself. Layer after layer, the pearl grows inside the shell.
Wild pearls are exceptionally rare. It is estimated that only one in 15.000 wild oysters contain a pearl. Therefore nearly all pearls are cultivated. This is done by inserting a small particle inside the shell. Usually the pearl gets harvested after about two years.
Japan is quintessential pearl-country. It was there that the cultivating process has been perfected.
The ideal pearl is perfectly round and smooth. Most pearls have a white color although other colors do exist.