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Various structures characterize ductile faults. The rocks of ductile faults are called mylonites. In the case of rocks rich in quartz (granite for example), this one is deformed in a ductile manner and constitutes a matrix which encompasses minerals which deform in a brittle manner (clasts: feldspar, ferromagnesian,…). Depending on the proportion of matrix relative to the clasts, the intensity of the ductile deformation can be evaluated. The geometry of the peri-clastic structures makes it possible to define the sense of the shear which gave rise to these singular rocks.