Pearl Formation and Structure

What usually causes a pearl to form inside an oyster?

• A special type of seed planted by humans.

• A small irritant, like a piece of food or sand, getting inside the oyster.

• The oyster's natural growth process.

• A chemical reaction with saltwater.

What is the protective structure an oyster forms around an irritant?

• A shell casing

• A pearl sac

• A mantle layer

• An aragonite shield

What material makes up the layers of a pearl, giving it its shiny appearance?

• Calcite

• Protein glue

• Nacre

• Sand

Why are most naturally formed pearls not perfectly round?

• The oyster's shell is not perfectly round.

• The irritant inside the oyster is usually irregular in shape and moves around.

• The water currents in the ocean prevent them from becoming round.

• Oysters prefer to make pearls of different shapes.