Pearls develop as nacre 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?”
Dr Julyan Cartwright from the CSIC – Universidad de Granada in Spain and colleagues 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. “The answer may be relatively simple — with developing pearls having a saw-toothed, or ratchet-like, surface,” Dr Cartwright and his colleagues said.
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 concluded.
Via David Simpson, Dr. Stefan Gruenwald, India Rows of The Pearl Girls