Breccia: Fault rocks composed of angular fragments (clasts) of wall rock set in a finer-grained matrix of crushed wall-rock material. Matrix is subordinate to clasts, comprising less than 30% of the breccia.
Cataclasite: A fault rock whose grain size is similar to gouge, typically less than 0.1 mm, although it can contain up to 50% visible through still fine-grained clasts. Typically it is ultra-fine-grained and nearly glassy in appearance.
Decollement: The detachment of the upper cover from its substratum.
Denudational Fault: A low angle normal fault which places high-level younger rocks on top of deeper-level older rocks.
Microbreccia: A breccia composed of clasts that are smaller than 1 mm but greater than 0.1 mm.
Mylonite: Rocks formed as a result of ductile deformation, which occurs in crustal rocks at temperatures usually exceeding 250-350 degrees C. This usually takes place in a ductile shear zone. The mylonite usually consists of more than one mineral, and the minerals behave differently to the shearing. Commonly a quartz will "flow" or be have plastically and feldspar crystals will behave brittlely and break into chips. The fabric thus created will contain feldspar crystals wrapped in quartz ribbons.
Ultracataclasite: A cataclasite that is the very finest, hardest, most glassy of the cataclasites.
Ultramylonite: A more thoroughly deformed and fine-grained rock containing more than 90% matrix and less than 10% relict grains. Ultramylonites are mylonites taken to the edge of recognition.
Strain within shear zones can have components of distortion ( change in shape) or dilation (volume change).