Researchers have discovered how oysters and other mollusks grow such symmetrical pearls, such as the pearls of Akoya pearl oyster, as shown in the picture. This discovery may inspire new materials for solar panels and spacecraft.

For centuries, researchers have been puzzled by how oysters grow amazingly symmetrical, perfectly round pearls around irregularly shaped sand or debris. Now, a team has proven that oysters, mussels, and other molluscs use complex processes to grow gems, which follow the mathematical rules common in nature.

When an irritant is trapped in a mollusk, a pearl is formed, and this animal protects itself by building a smooth layer of minerals and protein (collectively called the nacre) around it. According to the analysis published in the Proceedings of the National Academy of Sciences on October 19, each new nacre layer built on this asymmetric center accurately adapts to its previous nacre and eliminates irregularities. A round pearl was formed.

Laura Otter, a biogeochemist at the Australian National University in Canberra, said: "Nacre is a very beautiful, iridescent, shiny substance. We see it inside some shells or outside of pearls. ."

Otter and her colleagues found that the symmetrical growth of pearls during the deposition of the nacre depends on the balance of two basic abilities of mollusks. It can correct the growth distortion that occurs when the pearl is formed and prevent these changes from spreading on the multiple layers of the pearl. Otherwise, the resulting gems will be unbalanced.

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In addition, molluscs regulate the thickness of the nacre, so if one layer is particularly thick, the subsequent layers will be thinner accordingly (SN: 3/24/14). This helps the pearl maintain a similar average thickness in its thousands of layers, making it look perfectly round and uniform. Without this constant adjustment, pearls may resemble layered sedimentary rocks, magnifying small defects that detract from their spherical shape.

Researchers studied keshi pearls collected from Akoya pearl oysters (Pinctada imbricata fucata) at a pearl farm on the eastern coast of Australia. They used a diamond wire saw to cut the pearl into cross-sections, and then polished and inspected the gemstone using Raman spectroscopy. Raman spectroscopy is a non-destructive technique that allows them to characterize the structure of the pearl. For one of the pearls shown in the paper, they calculated 2,615 layers with a deposition time of more than 548 days.

Analysis shows that the fluctuations in the thickness of the nacre show a phenomenon called 1/f noise or pink noise, in which seemingly random events are actually interrelated. In this case, the formation of the different thickness of the nacre may appear to be random, but it actually depends on the thickness of the previous layer. The same phenomenon also plays a role in seismic activity: the rumble of the ground seems to be random, but it is actually related to the recent seismic activity. Co-author Robert Hofden, a materials scientist and engineer at the University of Michigan in Ann Arbor, said that pink noise can also appear in classical music, even when monitoring heartbeat and brain activity. Hofden said that these phenomena "belong to a general category of behavior and physics."

Pupa Gilbert, a physicist who studies biomineralization, said this is the first time researchers have reported that "the nacre will repair itself. When a defect occurs, it will repair itself in several [layers] without the need for external support or Template." The University of Wisconsin-Madison did not participate in this study. "Nacre is a superior material than we have appreciated before."

Otter notes: "These humble creatures are making an ultra-light and ultra-tough material, which is easier and better than all our technologies." The nacre is made only of calcium, carbonate and protein, "than The material from which it is made is 3,000 times harder."

Hofden added that this new understanding of pearls may spur the creation of "next-generation super materials," such as more energy-efficient solar panels or tough, heat-resistant materials optimized for use in spacecraft.

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