The three great classes of rock types, namely sedimentary, igneous and metamorphic, are defined strictly on a genetic basis and represent records of the sedimentary, magmatic and metamorphic processes taking place in and, on the surfaces of, rocky planets. The genetic basis of the three great classes is best shown by a review of the history of understanding of their origin. The tri-partite subdivision of the major rock types omits, however, one major class, namely those rocks formed dominantly through structural processes, herein called structural rocks. Omission of this major class of rock type has resulted from the late recognition of the incidence frequency, and the large scale, of the structural processes generating rock types distinct from those included in the other three classes. Another reason for the late recognition of the structural rocks is the still prevalent confusion of structural rocks with metamorphic rocks. Structural rocks form entirely along fault zones, whose sizes may range from those barely mappable at usual mapping scales to transcontinental shear zones of thousands of km of offset and subduction zones, along which displacement magnitudes may reach tens of thousands of km. Structural rocks are conveniently divided into fault rocks and melanges. Broken and disrupted formations and chaos structure constitute intermediary types between the two. A different classification, used in this paper, divides them into coherent and incoherent structural rocks. The coherent ones are further subdivided into brittle and ductile structural rocks. Structural rocks may become metamorphosed after formation or they may originate in metamorphic conditions, which makes their recognition difficult. They constitute rock bodies of various sizes, herein called keiroliths (Greek, kappaepsilonirhoomega = to shear and lambdaithetaos = rock), ranging from insignificant volumes along small faults, that are usually not mapped separately from the fault trace, to immense complexes forming considerable portions of entire continents.