How do oysters make pearls?

Explore how oysters use calcium carbonate to create pearls, and how this chemical compound creates a vast array of other materials.

Despite their iridescent colors and smooth shapes, pearls are actually made of the exact same material as the craggy shell that surrounds them. Pearls, urchin spines, the shells of mussels, snails and clams, even coral— all these structures are made out of the same chemical compound: calcium carbonate. So how does this single ingredient form such a vast array of materials? Rob Ulrich investigates.