How Do Oysters Make Pearls?

A pearl starts with living tissue

A pearl is a biological product, rather than a stone polished inside a shell. Misplaced shell-producing tissue can create a pearl sac after a parasite enters or the animal is injured. The sac supplies the material that builds the pearl. ^[1]

Layers create the familiar luster

Nacre contains aragonite, a form of calcium carbonate, together with organic material. Repeated deposition produces a layered structure. Light interacting with those layers contributes to the sheen of a nacreous pearl; the animal does not manufacture a finished sphere at once. ^[2]

Cultured pearls still grow in animals

Pearl farmers initiate pearl growth through a deliberate intervention. The mollusk then makes the coating through its own biological processes. Cultured pearls are therefore different from imitation beads, whose pearly surface is manufactured without a living pearl-producing animal. ^[1]

Not every oyster makes a jewelry pearl

Pearl oysters differ from the oysters commonly served as food. Other mollusks can produce pearls too, but not all use nacre or create the smooth, lustrous gems associated with necklaces. Shape and surface vary, so a natural pearl need not be perfectly round. ^[2]

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