Crenulation cleavage is found in rocks which have undergone multiphase deformation. It is due to folding of the original cleavage during subsequent episodes of deformation. It gives the surface of the slate a crinkled or crenulated effect. It is one of the characteristics commonly used to identify Scottish Easdale slate. However it is not conclusive as it is also found in Ballachulish slate, In most cases polyphase deformation distorts the original cleavage making the rock uneconomic for slate production.