A natural pearl created by a grain of sand is such a common misconception that I feel this is an adequate post.
I see so much literature about pearls, and so often I see people describing natural pearls as an occurrence initiated by a grain of sand. This is just not true!
There is absolutely no documentation of someone finding a grain of sand in the center of a natural pearl. Sand will not dissolve nor dissipate. If the sand induced an oyster to create the pearl it would stand to reason that the pearl would still contain the sand after it had been harvested.
Also, I love to eat oysters, and as I am sure all of your know they very often have sand in them if not thoroughly cleaned. If sand induced pearls would not many, many more oysters naturally have a pearl inside, instead of 1 in 10,000 of a pearl producing variety?
Pearls are almost certainly induced by a parasite or other organic matter that has made its way into the oyster.
I just had to get this off my chest!