You can't talk about pearl symbolism without starting with Sandro Botticelli's painting of The Birth of Venus.

The theme of the painting originates in Ovid's Metamorphoses in Latin literature. Venus stands naked on an oyster shell, seemingly born as a rare and beautiful pearl. Her hair and roses are gently blown by Zephrus, the wind god. On her right, a wondrous handmaiden, thought to be Hora, a Grace of spring, brings a cloak of flowers to wrap her. Venus, the goddess of love and beauty is pictured born of purity as rare and perfect as a pearl. Pearls are thought to be the tears of the goddess as well.