Concept:Pearls are formed inside the shell of certain mollusks, primarily oysters, as a natural defense against irritants.
Explanation:Pearls are harvested from oysters, specifically marine oysters and freshwater mussels.
When an irritant like a grain of sand or parasite enters the oyster's shell, the oyster secretes layers of nacre (mother-of-pearl) around it.
This process forms a natural pearl.
Cultured pearls are produced similarly by farmers intentionally inserting an irritant into the mollusk.
Pearls are composed of aragonite and conchiolin in thin layers.
The quality depends on the thickness and number of layers, affecting refraction, reflection, and diffraction of light.
Oysters are the primary source of harvested pearls.
Answer:Oyster.