No one really knows how this theory began. It certainly has a romantic appeal, but no scientific basis.

What is the true story?

It is true that there is an "irritant" that causes a mollusk to lay down layers and layers of nacre. Mollusks literally live in the sand and with the movement of the ocean waters, millions of grains of sand filter through mollusks. They are filter feeders that open their shells to feed on nutrients that float by.

If a pearl was formed every time a grain of sand entered a mollusk, pearls would not be rare. Mollusks spit" out sand that floats inside. But, every once in a while, a pesky irritant like a worm or parasite will bore through the shell and lodge itself inside and then the soft tissue of the mollusk will start laying nacre over the intruder and it will create a truly natural pearl. this is the way a NATURAL pearl is created. More later on how a CULTURED pearl is formed.

So, hold you head high and explain this to the next person who regales you with the Grain of Sand Myth.