The crystal structure of pearls and related shellfish's shells

In this article we explored the crystal structure of a few pearls and shellfish's shell of fresh water and sea water, and found that pearls and nacreous layer (perhaps and prismatic layer) of shells are all the same:CaCO₃, orthorhombic system, aragonite structure and the value of lattice spacings are almost identical. This shows that the pearls of fresh water and sea water are all the same in nature.