The reason the atoms do this is the same reason why any two chemicals react: within each crystal, all of the atom’s electrons are part of a stable chemical bond with its neighbors—they are, as it were, “occupied”—but at the edges and surfaces of the crystal, there are “unoccupied” electrons, ones that have no other atoms to bind to, the equivalent of loose ends. For this reason, all of the atoms in a crystal seek a position within the body of the crystal rather than at its surface; or, put another way, those atoms at the surface of the crystal are unstable, available, and liable to relocate if
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