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shells protect themselves from predators by using a two layered system, one of which is nacre. Nacre constitutes the inner layer while the other, outer, layer is made from calcite. The latter is hard and thus prevents any penetration through the shell, but is subject to brittle failure. On the other hand, nacre is softer and can uphold inelastic deformations, which makes it tougher than the hard outer shell. The mineral found in nacre is aragonite, CaCO₃, and it occupies

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