First a fault breccia will form, but if the grinding continues the rock becomes fault gouge.

Fault breccia is a medium to coarse-grained cataclasite.

Sometimes a distinction is made between fault gouge and fault breccia, the first has a smaller grain size.

Cataclasite grades into fault breccia as the percentage of visible clasts increases to more than 30%.

Fault gouge forms in the same way as fault breccia, the latter also having larger clasts.

Fault breccia has no cohesion, it is normally an unconsolidated rock type, unless cementation took place at a later stage.

Examples being fault gouge, fault breccia, and foliated gouge.

Fault breccia is a fault rock that consists of large fragments of rock in a fine-grained matrix.

Fault breccia is a tectonite formed by localized zone of brittle deformation (a fault zone) in a rock.

U-Pb mineralisation occurs in a fault breccia in Devonian sediments at Mill of Cairston near Stromness on Orkney.

The fault rock within the fault zone shows a long and complex history of movement with the development of fault breccia, mylonite and pseudotachylite, indicating faulting at a wide range of crustal levels.

Zones of fault breccia and fault gouge in rocks can be a hazard for the construction of tunnels and mines, as the non-cohesive zones form weak places in the rock where a tunnel can collapse more easily.