Cleats in coal
Cleats are naturally occurring orthogonal joints in coal. They occur as two perpendicular sets of fractures. The dominant cleat is called the "face cleat." It is oriented parallel to the maximum horizontal compressive stress at the time of coalification when the cleats formed. The subordinate cleat, called the “butt cleat,” forms at near right angles to the face cleat in the minimum stress orientation. In many cases, face-cleat orientation is similar to the orientation of other fractures in mine roofs, but this is not always the case. Cleat orientation commonly is related to local structural orientations in Appalachian and Midcontinent coal fields (McCulloch and others, 1974; Kulander and Dean, 1993; Laubach and others, 1998).
