Among the four basic classes of fractures, faults are the most complex structures involving different failure mechanisms. For example, shear bands are faults initiated by the localization of strain into narrow bands. Yet at more mature stages shear bands include slip surfaces which are prototypical faults. As discussed in great detail under 'Faults' and 'Growth of Faults,' pressure solution and brittle failure structures are common in fault zones. Also keep in mind that many faults are hybrid in terms of their displacement discontinuities as illustrated in 'Assemblages of Different Types of Faults.'