Lithologic Control on Cleavage Spacing

Photo
Slaty cleavage in the Martinsburg Slate, Ramsayburg, New Jersey. Bedding dips from upper right to lower left, and shows up as dark and light color bands. Cleavage dips from upper left to lower right. Cleavage is most widely spaced in the coarser, lighter-colored units (e.g., red arrow) and is most closely spaced in the finer-grained, darker-colored units (e.g., blue arrow). There is no cleavage refraction, indicating that this outcrop is located in the hinge region of a larger fold. Because cleavage and bedding dip in opposite directions, bedding is not overturned. This outcrop is a stop on the Valley-and-Ridge field trip. Photo credit: Roy W. Schlische.