Mylonite

mylonite [′mī·lə‚nīt]

(petrology)

A hard, coherent, often glassy-looking rock that has suffered extreme mechanical deformation and granulation but has remained chemically unaltered; appearance is flinty, banded, or streaked, but the nature of the parent rock is easily recognized.

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Mylonite 

finely ground, crushed rock formed by the movement of rock masses along the surface of tectonic faults. As a result of great pressure, the rocks (granite, gneiss, schists, quartzite) are crushed and ground into a compact state. Microscopic analysis makes possible the identification of finely ground mica flakes and minute quartz and feldspar fragments in the finely pulverized mass, which is made up of the softer minerals of the primary rock and sometimes such new formations as sericite and zoisite. Unlike cataclasis, mylonitization represents the final stage in the crushing of rock into microscopic form. Mylonite zones are located along the major regional thrust faults in the Urals, Tien-Shan, the Caucasus, and the Altai. These zones are several hundred meters wide and extend several dozen kilometers.

REFERENCE

Polovinkina, Iu. I. Struktury i tekstury izverzhennykh i metamorficheskikh porod, vol. 2, part 2. Moscow, 1966.