Researchers at the University of Granada note flawless and highly prized pearls have perhaps the most perfectly spherical shape among all the objects in nature that are visible without a microscope.
Writing in a journal of the American Chemical society, they say the spherical shape results from a developing pearl's saw-toothed, or ratchet-like, surface, a texture that creates forces that cause the pearl to turn inside the oyster's tissues in response to movements in the environment.
The ongoing movement results in a spherical build-up of nacre (mother of pearl) deposited around a grain of sand or other foreign object in shellfish.
The rotating pearls may be unique example of a natural ratchet, the scientists said.
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