Fissile refers to a rock’s ability to be easily split along closely spaced planes, typically due to the alignment of platy minerals or the presence of bedding or cleavage. Fissile rocks, such as shale, are important in understanding sedimentary structures, stratigraphy, and the mechanical behavior of rocks under stress.
Reference: Tucker, M. E. (2003). Sedimentary Rocks in the Field: A Practical Guide. Wiley-Blackwell.