Although schist breaks into sheets

Although schist breaks into sheets like
slate, and is sometimes used as roofing
tiles where slate is scarce, it does not
cleavequite as easily. The extreme heat and
pressure mean the layers are more tightly
knitted together. They are often also slightly
wrinkled, or 'crenulated', similarly to phyllire
buteven more so. In some schists, these
contortions can become quite dramatic.