When a crystal of a binary oxide is cleaved to generate two new surfaces, each solid's charge remains neutral. However, the structure of the two newly created surfaces may or may not be the same. If the structures are identical, the surface will be dipoleless and is considered a nonpolar surface. If the structures are different, the surface will have a strong dipole and is considered a polar surface. Examples of nonpolar surfaces include the rocksalt (100) surface, the rutile (100), (110) and (001) surfaces and the pervoskite (100) surface. An example of a polar surface is the rocksalt (111) surface. In general, a polar surface is less stable than a nonpolar surface because a dipole moment increases the surface Gibbs energy. Also, oxygen polar surfaces are more stable than metal polar surfaces because oxygen ions are more polarizable, which lowers the surface energy.