Despite extensive research on fault rocks, and on their commercial importance,there is no non-genetic classification of fault breccias that can easily beapplied in the field. The present criterion for recognizing fault breccia ashaving no ‘primary cohesion’ is often difficult to assess.Instead we propose that fault breccia should be defined, as with sedimentarybreccia, primarily by grain size: with at least 30% of its volume comprisingclasts at least 2 mm in diameter. To subdivide fault breccias, we advocate theuse of textural terms borrowed from the cave-collapse literature –crackle, mosaic and chaotic breccia – with bounds at 75% and 60%clast content. A secondary breccia discriminant, more difficult to apply in thefield, is the ratio of cement to matrix between the clasts. Clast-size issuesconcerning fault gouge, cataclasite and mylonite are also discussed.
