Throughout history, there have been many speculations on the origin of pearl.  Romantic poets believed pearl originated from tears of angels, tears of water nymphs. 

‘The liquid drops of tears that you have shed,
Shall come again, transform’d  to orient pearl,’      Shakespere

‘The pearls that long have slept,
These were tears by Naiads wept’                   Sir Walter Scott

As the luster of pearl resembles the sparkling dewdrop first exposed to the sun’s rays, the ancients believed pearls are formed from drops of dew or rain.  Legend has it that at certain times of the year, pearl oysters rise to the water surface in the morning, open their shells to take in the dew drops, then the warmth of the sunlight and the breath of air will transform the dew drops into pearls.  The amount of sunlight and air received will determine the color and luster of the pearl.  This dew drop theory has been accepted for centuries by scholars in Europe.

In late 17^th century, Naturalists began a more scientific theory for the origin of pearl.  It was believed that pearls were formed from the eggs of the oyster.  In mid 18^th century, Naturalists such as Reaumur and Linnaeus discovered that the pearl and the oyster shell are of the same material, that the pearl is built of concentric layers.  However, experiments also showed that the growth of pearl requires some foreign body introduced into the shell, this irritation becomes the nucleus, and causes the shell to secret layers of substance called nacre around the foreign body. In the course of years, this results in a pearl or multiple pearls.    Pearls are found to form not only in oysters, but also commonly in mussels and other mollusks or shell animals.

Pearls are generally round, but the shape of the nucleus and the positioning of the nucleus can result in other shapes such as pear, elongated, dog toothed, and many other varieties.

Pearls can also come in different shades depending on the ingredients of the water, the health of the shell, and accidents of various kinds.

The parasitic origin of pearl formation is the forerunner of the cultured pearl industry.

It appears that there is nothing new under the sun.  As early as 14^th century, the Chinese have been found to culture pearly objects and even images of the Buddha.