Pearls form when displaced mantle tissue builds a pearl sac and layers nacre — aragonite platelets bound with conchiolin — over months. The grain-of-sand story, corrected by a pearl farmer.

A working farmer's tour of the Pinctada genus — Pinctada maxima, Pinctada margaritifera and Pinctada fucata compared as living animals, and how each one's biology decides the pearls it grows.