[geology] Fissility or Fissionability (American English) refers to the property of rocks to split along planes of weakness into thin sheets. This is commonly observed in shales, which are sedimentary rocks, and in slates and phyllites, which are foliated metamorphic rocks. The fissility in these rocks is caused by the preferred alignment of...
ability to be split
• (n.) Quality of being fissile.
A general term for the property possessed by some rocks of splitting easily into thin layers along closely spaced, roughly planar, and approximately parallel surfaces, such as bedding planes in shale or cleavage planes in schist; its presence distinguishes shale from mudstone. The term includes such phenomena as bedding fissility and fracture cleav...
The property exhibited on fissile rocks or minerals that is responsible for the splitting along parallel layers. Fissility exhibited on minerals is either cleavage or parting.
Fis·sil'i·ty noun Quality of being fissile. 
see shale.