What is "fault gouge"

n. (context geology English) Accumulated crushed rock debris which is the product of the movement of the rocks on each side of a fault.

Fault gouge is an unconsolidated tectonite (a rock formed by tectonic forces) with a very small grain size. Fault gouge has no cohesion, it is normally an unconsolidated rock type, unless cementation took place at a later stage. A fault gouge forms in the same way as fault breccia, the latter also having larger clasts.

Gouge filled faults can be weak planes in rock masses. If compressive stresses are enough these can cause compressive yielding or eventually rock fracture.