Ultracataclasite is a type of fault rock formed by intense mechanical grinding and crushing of rocks along a fault zone, resulting in a very fine-grained, cohesive rock. This material is significant in structural geology for understanding fault mechanics, earthquake processes, and the evolution of fault zones.
Reference: Sibson, R. H. (1977). “Fault Rocks and Fault Mechanisms.” Journal of the Geological Society, 133(3), 191-213.