Pearls, urchin spines, the shells of mussels, snails and clams, even coral— all these structures are made out of the same chemical compound: calcium carbonate.

珍珠、海胆刺、贻贝、蜗牛和蛤蜊的壳，甚至珊瑚——所有这些结构都是由相同的化合物构成的：碳酸钙。