Fault breccia

The grinding and milling occurring when the two sides of the fault zone moving along each other results in a material that is made of loose fragments.

Secondary minerals such as calcite, epidote, quartz or talc can precipitate from the circulating groundwater filling the voids and cementing the rock.

However, when the tectonic movement along the fault zone continues the cement itself can be fragmented leading to a new gouge material containing neoformed clasts.

Deeper in the Earth's crust, where temperatures and pressures are higher, the rocks in the fault zone can still brecciate, but they keep their internal cohesion.

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