How pearls get their perfect spherical shape



Washington: The mystery of how pearls form into the most perfectly spherical large objects in nature may have an unlikely explanation.

Julyan Cartwright, Antonio G. Checa and Marthe Rousseau point out that the most flawless and highly prized pearls have perhaps the most perfectly spherical, or ball-like, shape among all the objects in nature that are visible without a microscope.

Pearls develop as nacre (mother of pearl) and other liquids accumulate around grains of sand or other foreign objects inside certain oysters and other shellfish. But how do pearls grow into such perfect spheres?

The answer, they say, may be relatively simple - with developing pearls having a saw-toothed, or ratchet-like, surface.

That texture generates forces that make the pearl turn inside the oyster's tissues in response to movements in the environment.

The result is a spherical build-up of nacre and other textures.

Rotating pearls are a perhaps unique example of a natural ratchet, the scientists said.

The study is published in the ACS' journal Langmuir.

ANI