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mylonite Rock produced in zones of tectonic dislocation, e.g. fault and shear zones. Mechanical crushing and grinding or cataclasis produces a rock that has a foliation which is often crude but which is sometimes very well developed, and that has a much finer grain size than its precursor. Mylonite is well laminated and often hard and splintery. The name literally means ‘milled rock’ from the Greek mylon, a grinding mill. See DYNAMIC METAMORPHISM.